KR102113212B1 - Flash memory system and control method thereof - Google Patents

Abstract

Flash memory control method according to an embodiment of the present invention, determining the data type as hot data or cold data according to the update time interval of the write-requested data to be stored in the flash memory, according to the determined data type Storing the write-requested data in a hot block pool or a cold block pool provided in a flash memory, and the data retention time is the first data retention time or the second data retention time according to the block pool in which the write-requested data is stored. Allocating, and updating the write time of the stored write-requested data to the current write time, the first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool It is characterized by.

Description

Flash memory system and control method thereof

The present invention relates to a memory control technology, and more particularly, to a flash memory system and a control method thereof.

2. Description of the Related Art Semiconductor memory devices are largely classified into volatile memory devices and non-volatile memory devices. Volatile memory devices have a fast read and write speed, but have a disadvantage in that the stored content disappears when the external power supply is cut off. On the other hand, the non-volatile memory device preserves its contents even when the external power supply is interrupted. Therefore, a nonvolatile memory device is used to store contents to be preserved regardless of whether power is supplied. In particular, among non-volatile memories, a flash memory has a high degree of integration as compared to a conventional EEPROM (Electrically Erasable Programmable Read-Only Memory), which is very advantageous for application as a large capacity auxiliary storage device.

Recently, flash memory has been used as a storage medium to replace a hard disk drive (HDD) due to advances in technology and a reduction in the price of a flash memory device. The aforementioned storage device is also referred to as a solid state drive or a solid state disk. Hereinafter, it will be referred to simply as an SSD. SSDs are capable of inputting and outputting data at high speed, but have a very low mechanical delay or failure rate. In addition, the SSD has an advantage that data is not easily damaged by external shocks, heat generation, noise and power consumption are small, and it is possible to reduce the size and weight. Accordingly, the demand for SSDs that do not use mechanically rotating platters is rapidly increasing according to low-power and high-capacity mobile trends. However, the NAND flash-based SSD has a disadvantage in that the number of data writing and erasing (P / E cycle) is limited.

With the popularization of NAND flash memory-based SSDs, SSDs are also widely adopted as storage devices in enterprise-class data centers. NAND flash memory is used not only as a personal computer but also as a storage device for enterprise-class servers due to its low power and high performance. In line with this trend, the need for a NAND flash memory-based SSD that can store large amounts of data is also increasing. To this end, MLC (Multi Level Cell) and TLC (Triple Level Cell) flash memories that store 2 bits and 3 bits in one cell have appeared. However, they have the disadvantage that durability is greatly reduced.

On the other hand, in relation to the technology for determining the data stored in the flash memory, the prior art includes a write request size based technique and an update frequency based technique. Based on the size of the write request, the write request size-based technique is divided into hot data for small sized write requests and cold data for large sized write requests. In addition, the update frequency-based technique uses the LRU (Least Recently Used) technique to classify data in which a write operation has occurred among recently stored data into hot data and other data into cold data.

Korean Patent Publication No. 10-2013-0076429 (published on July 8, 2013)

However, when distinguishing between hot data and cold data as in the prior art, the prior art cannot make the most of the improved durability of the flash memory. This is because, in the case of the prior art, even in the case of data of a write request having a small size, the update was not frequent. In addition, when the LRU technique was used, there were many cases where long data retention time was required even though it was classified as hot data. In addition, in the case of an SSD for storing large-scale data, MLC and TLC flash memories that store 2 or 3 bits in one cell are mainly used. However, they have the disadvantage of poor durability.

According to embodiments of the present invention, a flash memory is stored by determining a data type as hot data or cold data according to an update time interval of write-requested data, storing the data in a corresponding block pool, and allocating data retention time for each block pool. An object of the present invention is to provide a flash memory system and a control method for improving the lifespan of an equipped SSD.

According to an embodiment of the present invention, in a flash memory control method performed by a flash memory controller, according to an update time interval of write-requested data to be stored in the flash memory, hot data or cold data data) to determine the data type; Storing the write-requested data in a hot block pool or a cold block pool provided in the flash memory according to the determined data type; Allocating a data retention time as a first data retention time or a second data retention time according to the block pool in which the write-requested data is stored; And updating the write time of the stored write-requested data to the current write time, wherein the first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool. A flash memory control method can be provided.

The flash memory control method includes: checking whether a previous write time of the write-requested data is recorded; And if the previous write time is not recorded, determining the data type of the data requested to be written as cold data.

In the determining of the data type, the data type may be determined as hot data or cold data by comparing an update time interval between a previous write time of the write-requested data and a current write-request time with the first data retention time. have.

The determining of the data type may be determined as hot data if an update time interval between a previous write time of the write-requested data and a current write-request time is less than the first data retention time.

In the determining of the hot data or cold data, if the update time interval between the previous write time of the write-requested data and the current write-request time is equal to or greater than the first data retention time, it may be determined as cold data.

In the step of storing the write-requested data, if the previous data for the write-requested data is stored in a hot block pool or a cold block pool, the previous data stored in the block pool may be invalidated.

In the allocating step, the first data retention time set in the hot block pool may be adjusted according to a characteristic of an input / output (I / O) trace where the write requested data is generated.

The write-requested data whose data type is determined to be hot data may be at least one metadata generated due to application driving or file manipulation of a host connected through a host interface.

The write-requested data whose data type is determined to be cold data may be backup data generated due to a backup operation of a host connected through a host interface.

The flash memory may be a flash memory of any one of SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell) and QLC (Quad Level Cell).

According to another embodiment of the present invention, a flash drive having at least one flash memory, wherein the storage area of the flash memory is divided into a hot block pool and a cold block pool; And determining a data type as hot data or cold data according to an update time interval of data requested to be written to the flash drive, and storing the write-requested data in a hot block pool or a cold block pool, and storing the write-requested data. And a flash memory controller for allocating data retention time as a first data retention time or a second data retention time according to a block pool, and updating the write time of the stored write-requested data to the current write time, wherein the hot block pool A flash memory system may be provided, wherein the first data retention time set at is less than the second data retention time set at the cold block pool.

The flash memory controller may check whether the previous write time of the write-requested data is recorded, and if the previous write time is not recorded, determine the data type of the write-requested data as cold data.

The flash memory controller may determine the data type as hot data or cold data by comparing the update time interval between the previous write time of the write-requested data and the current write-request time with the first data retention time.

The flash memory controller may determine as hot data if an update time interval between a previous write time of the write-requested data and a current write-request time is less than the first data retention time.

The flash memory controller may determine that the update data interval between the previous write time of the write-requested data and the current write-request time is greater than or equal to the first data retention time.

When the previous data for the write-requested data is stored in a hot block pool or a cold block pool, the flash memory controller may invalidate the previous data stored in the corresponding block pool.

The flash memory controller may adjust a first data retention time set in the hot block pool according to a characteristic of an input / output (I / O) trace where the write requested data is generated.

The flash memory may be a flash memory of any one of SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell) and QLC (Quad Level Cell).

According to another embodiment of the present invention, a flash drive having at least one flash memory, wherein the storage area of the flash memory is divided into a hot block pool and a cold block pool; A timestamp calculation unit managing a write time of data stored in the flash memory and calculating an update time interval of write-requested data to be stored in the flash memory; And determining the data type as hot data or cold data according to the calculated update time interval, and storing the write-requested data in a hot block pool or a cold block pool, and maintaining data according to the block pool in which the write-requested data is stored. And a flash control unit that allocates a time as a first data retention time or a second data retention time, and the timestamp calculation unit updates the write time of the stored write-requested data to the current write time, and is set in the hot block pool. The first data retention time may be less than the second data retention time set in the cold block pool.

According to another embodiment of the present invention, in a flash memory control method in a flash memory system erased in units of blocks, data in the block unit in the flash memory controller-the data is a page unit of a flash memory And the block is composed of a plurality of pages-compares the time when the data is written and the updated time after the written data is written. ) And cold data (cold data); And discriminating and storing data having the same data type based on the discriminated data type in the flash drive, wherein the data retention time of the hot data in the flash memory controller is data of the cold data. A flash memory control method may be provided, characterized in that it is set shorter than the retention time.

The distinguishing step may include: recording a time at which the data is written in the block unit in the flash memory controller in a mapping table; And obtaining a difference between a time when the data is written and the updated time in the flash memory controller and comparing it with the data retention time of the set hot data, wherein the comparison result in the comparing step, the When the difference value between the updated time is smaller than the data retention time of the set hot data, it is classified as hot data, and when the difference value between the updated time is longer than the data retention time of the set hot data, it can be classified as cold data. .

In the storing step, the divided hot data may be stored in a hot block pool that is a storage area of the hot data, and the cold data may be stored in a cold block pool that is a storage area of the cold data.

In the flash memory control method, when the ratio of the size of the storage area of the hot data is less than or equal to a predetermined value in consideration of the ratio of the storage area of the flash drive to the storage area of the hot data, the size of the storage area of the hot data And the data retention time of the hot data.

According to another embodiment of the present invention, in a flash memory system erased in units of blocks, the data in units of blocks-the data has a page unit of flash memory, and the blocks are composed of a plurality of pages. Composed-Compares the time when the data is written and the updated time after the written data is written, and the type of the data is divided into hot data and cold data. Flash memory controller; And a flash drive having at least one flash memory and classifying and storing data having the same data type based on the distinguished data type, wherein the data retention time of the hot data in the flash memory controller is maintained. ) May be set to be shorter than the data retention time of the cold data, and a flash memory system may be provided.

1 is a view showing the configuration of a flash memory system according to an embodiment of the present invention.
2 is a flowchart of a method for controlling a flash memory performed by a flash memory controller according to an embodiment of the present invention.
3 is a detailed flowchart of a flash memory control method performed by a flash memory controller according to another example of the present invention.
4 is a view illustrating a determination operation of hot and cold data performed by the flash control unit of the flash memory controller according to an embodiment of the present invention.
5 is a diagram illustrating a data storage operation performed by a flash drive in a flash memory system according to an embodiment of the present invention.
6 is a diagram showing SSD variable values used in simulation of a flash memory control method according to an embodiment of the present invention.
7 is a view showing a comparison of the life of the SSD, when applying the prior art and an embodiment of the present invention.
8 is a view showing a comparison of response time when applying the prior art and an embodiment of the present invention.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component. The term and / or includes a combination of a plurality of related described items or any one of a plurality of related described items.

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but there may be other components in between. It should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the overall understanding in describing the present invention, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted.

1 is a view showing the configuration of a flash memory system according to an embodiment of the present invention.

As illustrated in FIG. 1, the flash memory system 100 according to an embodiment of the present invention includes a host interface 110, a central processing unit 120, a buffer memory 130, a flash memory controller 140 and a flash Drive 143. Each component is electrically connected through a control bus or a data bus, and can perform data communication.

First, the host interface 110 provides an interface with the host system 10. For example, in the case of a flash memory system such as an SSD having a SATA interface, the host interface 110 processes a SATA physical layer (Phy Layer) and a link layer (Link Layer). The flash memory system 100 may be connected to the host system 10 through a wired or wireless host interface. The host interface 110 may include one of various interface protocols such as USB, MMC, PCI-E, SAS, SATA, PATA, SCSI, ESDI, and IDE.

The central processing unit (CPU, 120) controls the overall operation of the flash memory system 100 in response to a request from the host system 10. The central processing unit 120 receives various control information required for a read operation and a write operation from the host interface 110. For example, when a command is input from the outside, it is stored in the host interface 110. The host interface 110 notifies the central processing unit 120 that a read or write command has been input according to the stored command.

Although the central processing unit 120 is shown in one configuration, it may be composed of two or more multi-processors. Each of the plurality of multi-processors constituting the central processing unit 120 may divide and process a control operation. That is, the flash memory system 100 may perform multi-tasking by a plurality of multi-processors. In addition, the flash memory system 100 including a plurality of multi-processors may perform parallel processing. By parallel processing, the flash memory system can realize high performance even when driven by a relatively low frequency clock. The central processing unit 120 may identify write-requested data that is requested to be written from the host system.

The buffer memory 130 temporarily stores data transmitted from the host system 10 or data to be transmitted to the host system 10. In addition, the buffer memory 130 stores Flash Translation Layer (FTL) information. The Flash Translation Layer (FTL) stored in the buffer memory 130 is operated by the central processing unit 120, address mapping management, wear-leveling management of the flash memory, and unexpected power It is used to manage data retention due to blocking. The buffer memory 130 may be formed of a DRAM buffer. The buffer memory 130 may include non-volatile RAM and volatile RAM. The data requested to be written to the flash drive 143 is temporarily stored in the buffer memory 130 and is stored in a nonvolatile RAM or volatile RAM.

The data requested to be written may be temporarily stored in the non-volatile RAM, and is written to or stored in the flash drive 143 after the temporary storage. At this time, the central processing unit 120 may transmit a host command processing signal (Complete) to the host system 10 as soon as the input data is requested to write to the non-volatile RAM.

The flash memory controller 140 processes flash memory commands such as read, write, and erase, and data transmission to the flash drive 143. In addition, a flash memory channel exists to connect the flash drive 143.

The flash drive 143 is a storage medium of the flash memory system 100 and may include a plurality of NAND type flash memories (144) having a large storage capacity. The flash drive 143 may be composed of a plurality of memory devices. Although NAND flash memory is described as an example of a storage medium, it may be configured with other nonvolatile memory devices. For example, PRAM, MRAM, ReRAM, FRAM, NOR flash memory, etc. may be used as a storage medium, and a flash memory system in which heterogeneous memory devices are mixed may also be applied. Also, a volatile memory device (eg, DRAM) may be included as a storage medium.

On the other hand, the flash memory controller 140 determines the type of data whose update time interval of the write-requested data is shorter than the first data retention time set in the hot block pool as hot data. In addition, the flash memory controller 140 allocates the data retention time of the hot data to the first data retention time shorter than the second data retention time set in the cold block pool. Conversely, the flash memory controller 140 determines the type of data whose update time interval of the write-requested data is longer than the first data retention time set in the hot block pool as cold data. In addition, the flash memory controller 140 allocates the data retention time of the cold data as the second data retention time set in the cold block pool. That is, the flash memory controller 140 according to an embodiment of the present invention adjusts the data retention time of the cells constituting the NAND flash. As the data retention time is shortened, the number of erasing of cells may increase. Based on this, the flash memory controller 140 keeps the data retention time of data (hot data) having a short update interval short. On the contrary, the flash memory controller 140 may improve the lifespan of the SSD by providing data retention time of data (cold data) having a long update interval relatively longer than hot data.

Meanwhile, the flash memory controller 140 according to an embodiment of the present invention may include a timestamp calculation unit 141 and a flash control unit 142.

Hereinafter, a detailed configuration and operation of each component of the flash memory controller 140 according to an embodiment of the present invention of FIG. 1 will be described.

The timestamp calculator 141 manages the write time of data stored in the flash memory 144. In addition, the timestamp calculator 141 calculates an update time interval of write-requested data to be stored in the flash memory 144.

The flash control unit 142 determines the data type as hot data or cold data according to the update time interval calculated by the timestamp calculation unit 141 and stores the write-requested data in the hot block pool or cold block pool. Here, the flash control unit 142 may determine the data type as hot data or cold data by comparing the update time interval between the previous write time of the write-requested data and the current write-request time with the first data retention time. At this time, the flash control unit 142 may determine that the data is hot if the update time interval between the previous write time of the write-requested data and the current write-request is less than the first data retention time. On the other hand, if the update time interval between the previous write time of the write-requested data and the current write-request time is greater than or equal to the first data retention time, the flash control unit 142 may determine the cold data.

In addition, the flash control unit 142 allocates the data retention time as the first data retention time or the second data retention time according to the block pool in which the data requested to be written is stored. Here, the first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool. The flash control unit 142 records the time at which data is written for each block through the time stamp calculation unit 141. The flash control unit 142 compares the current write time with the next write time, that is, the update time, and classifies the data type into hot data and cold day.

The flash drive 143 includes a flash memory 144 divided into a hot block pool and a cold block pool. The flash drive 143 manages data stored in the hot block pool and cold block pool. The flash drive 143 stores the data having the same data type by classifying and storing data based on the data type classified by the flash control unit 142. Thereafter, in the case of hot data, the flash drive 143 shortens and stores the data retention time up to the first data retention time, thereby providing a high number of write and erase cycles (P / E Cycle).

Thereafter, the timestamp calculation unit 141 updates the write time of the stored write-requested data to the current write time.

Meanwhile, the flash control unit 142 may check whether the previous write time of the data requested to be written is recorded, and if the previous write time is not recorded, the data type of the data requested to be written may be determined as cold data.

In addition, if the previous data for the write-requested data is stored in the hot block pool or the cold block pool, the flash control unit 142 may invalidate the previous data stored in the corresponding block pool. The flash control unit 142 may adjust the first data retention time set in the hot block pool according to the characteristics of the input / output (I / O) trace where the write requested data is generated. The flash control unit 142 may adjust the storage area of the hot block pool in consideration of the ratio of the size of the storage area occupied by the hot data to the storage area of the hot block pool in the entire flash drive 143. For example, the flash control unit 142 considers the ratio of the size of the storage area of the hot data to the storage space of the entire flash drive 143, and when the ratio of the size of the storage area of the hot data is less than or equal to a predetermined value, the hot data storage area Can reduce the size of Alternatively, the flash control unit 142 may reduce the first data retention time allocated for the hot data.

The write-requested data whose data type is determined to be hot data may be at least one metadata generated due to application driving or file manipulation of the host system 10 connected through the host interface 110. The write-requested data whose data type is determined to be cold data may be backup data generated due to a data recording or data preserving operation in the host system 10 connected through the host interface 110.

The flash memory 144 may be a flash memory of any one of SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell) and QLC (Quad Level Cell).

Meanwhile, the flash memory system 100 according to another embodiment of the present invention will be described. In the flash memory system 100 according to another embodiment of the present invention, data is erased in block units.

The flash memory controller 140 compares the time when data is written in block units and the updated time after the written data is written. Here, the data has a page unit of the flash memory, and the block is composed of a plurality of pages. In addition, the flash memory controller 140 classifies data types into hot data and cold data.

The flash drive 143 includes at least one flash memory 144. The flash drive 143 stores data having the same data type separately based on the data type classified by the flash memory controller 140 and stores the data.

Here, the flash memory controller 140 sets the data retention time of the hot data to be shorter than the data retention time of the cold data.

2 is a flowchart of a method for controlling a flash memory performed by a flash memory controller according to an embodiment of the present invention.

In step S101, the flash memory controller 140 calculates an update time interval of write-requested data to be stored in the flash memory 144.

In step S102, the flash memory controller 140 determines a data type as hot data or cold data according to an update time interval of write requested data to be stored in the flash memory 144. Here, the flash memory controller 140 checks whether a previous write time of data requested to be written is recorded. As a result of the check, if the previous write time is not recorded, the flash memory controller 140 may determine the data type of the data requested to be written as cold data.

In step S103, the flash memory controller 140 stores data requested to be written in a hot block pool or a cold block pool provided in the flash memory 144 through the flash drive 143 according to the determined data type.

In step S104, the flash memory controller 140 allocates the data retention time as the first data retention time or the second data retention time according to the block pool in which the write-requested data is stored. Here, the first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool.

In step S105, the flash memory controller 140 updates the write time of the stored write-requested data to the current write time.

3 is a detailed flowchart of a flash memory control method performed by a flash memory controller according to another embodiment of the present invention.

In step S201, when a write request is generated from the host system, data requested to be written to the flash memory controller 140 through the host interface is received.

In step S202, the flash memory controller 140 checks whether there is a write time record of the data requested to be written in the time stamp calculation unit 141.

In step S203, if there is a write time record of the data requested to be written (S202), the flash memory controller 140 determines whether the update time interval of the data requested to be written is shorter than the first data retention time of the hot block pool. To confirm.

In step S204, if the update time interval of the check result (S203), the write-requested data is shorter than the first data retention time of the hot block pool, the flash memory controller 140 determines the write-requested data as hot data. That is, the flash memory controller 140 may compare the update time interval between the previous write time of the write-requested data and the current write-request time with the first data retention time to determine the data type as hot data or cold data. Specifically, if the update time interval between the previous write time of the write-requested data and the current write-request time is less than the first data retention time, the flash memory controller 140 determines as hot data, and the previous write time of the write-requested data And if the update time interval between the current write request time is greater than or equal to the first data retention time, it may be determined as cold data.

In step S205, the flash memory controller 140 checks whether previous data of the write-requested data determined as hot data is stored in the hot block pool or cold block pool of the flash memory 144.

In step S206, if the previous result of the check result (S205), the data requested to be written is stored in the block pool of the flash memory 144, the flash memory controller 140 invalidates the previous data of the corresponding block pool that is stored. (Invalid).

In step S207, the flash memory controller 140 stores the write request data in a hot block pool. On the other hand, if the previous data of the write-requested data is not stored in the block pool of the flash memory 144, the flash memory controller 140 immediately performs step S207 of storing the write-requested data in the hot block pool. At this time, the flash memory controller 140 allocates the data retention time as the first data retention time according to the hot block pool in which the data requested to be written is stored. Here, the flash memory controller 140 may adjust the first data retention time set in the hot block pool according to the characteristics of the input / output (I / O) in which the write requested data is generated.

In step S208, the flash memory controller 140 records a new write time through the timestamp calculator 141 in a data block to which the newly stored write-requested data belongs.

On the other hand, in step S209, if there is no write time record of the check result (S202) and write-requested data, the flash memory controller 140 discriminates the write-requested data into initial write data and determines it as cold data. Further, if the check result (S203), the update time interval of the write-requested data is not shorter than the first data retention time of the hot block pool, the flash memory controller 140 determines the write-requested data as cold data.

In step S210, the flash memory controller 140 checks whether previous data of the write-requested data determined as cold data is stored in a hot block pool or a cold block pool of the flash memory 144.

In step S211, if the previous data of the check result (S210) and the write-requested data is stored in the block pool of the flash memory 144, the flash memory controller 140 invalidates the previous data of the corresponding block pool that is stored. (Invalid).

In step S212, the flash memory controller 140 stores the write-requested data in a cold block pool. On the other hand, if the previous data of the write-requested data is not stored in the block pool of the flash memory 144, the flash memory controller 140 immediately performs step S212 of storing the write-requested data in the cold block pool. At this time, the flash memory controller 140 allocates the data retention time as the second data retention time according to the cold block pool in which the data requested to be written is stored.

Subsequently, the flash memory controller 140 performs step S208 of recording a new write time.

Meanwhile, a method of controlling a flash memory in a flash memory system erased in units of blocks according to another embodiment of the present invention will be described.

Flash memory control method according to another embodiment of the present invention is the time in which data is written (block) in the block unit in the flash memory controller 140 and the updated time after the written data (write) is written (write) Comparing and classifying the data type into hot data and cold data, and storing and storing data having the same data type based on the data type classified in the flash drive 143. It includes. Here, the flash memory controller 140 sets the data retention time of the hot data to be shorter than the data retention time of the cold data.

According to another embodiment of the present invention, a method for controlling a flash memory includes writing a time in which data is written in block units in the flash memory controller 140 to a mapping table and writing data in the flash memory controller 140 ( It may include the step of obtaining the difference between the time being written and the updated time and comparing it with the data retention time of the hot data. Here, the flash memory controller 140 classifies it as hot data when the difference between the updated times is less than the data retention time of the hot data, and when the difference between the updated times is greater than the data retention time of the hot data, as a result of the comparison. It can be classified as data.

The flash drive 143 may store the divided hot data in a hot block pool, which is a storage area of hot data, and store cold data in a cold block pool, which is a storage area of cold data. The flash memory controller 140 considers the ratio of the storage space of the hot data to the storage space of the flash drive 143, and when the ratio of the size of the storage area of the hot data is less than or equal to a predetermined value, the size of the storage area of the hot data and The data retention time of hot data can be adjusted.

4 is a view illustrating a determination operation of hot and cold data performed by the flash control unit of the flash memory controller according to an embodiment of the present invention. 5 is a diagram illustrating a data storage operation performed by a flash drive of a flash memory system according to an embodiment of the present invention.

An embodiment of the present invention will be described across two layers of the flash controller 140 and the flash drive 143 inside the SSD.

First, the flash memory controller 140 physically separates the flash drive 143 in which data is actually stored into two areas, a hot block pool and a cold block pool. The hot block pool stores only the hot data, and the cold block pool stores the remaining data. At this time, the hot block pool shortens the data retention time as much as only the hot data is stored, thereby increasing the number of storage and deletion (Program / Erase cycles, P / E Cycle).

For this separation, the flash control unit 142 distinguishes data types. The flash control unit 142 records the time at which data is recorded in each block using a time meter such as the time stamp calculation unit 141. Then, when data to be updated later occurs, the flash control unit 142 checks the update time interval of the corresponding data. If the update time interval is shorter than the first data retention time of the hot block pool of the flash drive 143, it is classified as hot data, otherwise it is classified as cold data. Through this, the flash memory controller 140 can effectively classify hot and cold data and prevent side effects of data integrity problems beyond the data retention time.

As shown in FIGS. 4 and 5, a case in which write request data P9 and other write request data P21 occurs will be described as an example.

First, it is assumed on the assumption that the current time is 100. In addition, it is assumed that the first data retention time set in the hot block pool is 36 (Short Retention Time = 36). Here, 100 or 36 is a number for the convenience of description, and is not limited to a specific time.

Looking at the write-requested data P9, the write-requested data P9 has a data update at the current time 100. Then, the flash memory controller 140 checks the block number and the previous write time of the previous data of the data P9 that is requested to be written through the timestamp calculator 141 as Blk # 2 and 85 hours. Then, the flash memory controller 140 calculates the update time interval (100-85 = 15) between the current time 100, that is, the write request time and the previous write time, and compares it with the first data retention time 36 (Short Retention Time = 36). Then, it is confirmed that the update time interval 15 is less than the first data retention time. Subsequently, the flash memory controller 140 determines the write-requested data P9 as hot data, invalidates the previous data P9 stored in the cold block pool Blk # 2, and rewrites the new hot block Blk # 1 in the hot block pool. The data requested to be written is stored in P9. In addition, the flash memory controller 140 allocates the data retention time as the first data retention time. Here, although the previous data was stored in the cold block pool, the write request data P9 is determined as hot data and is stored in the current hot block pool. As described above, the data requested to be written is stored in the hot block pool, and when it is determined as cold data, it may be stored in the cold block pool. In addition, the flash memory controller 140 updates the previous write time 85 of the write-requested data P9 to the current write time 100.

Next, looking at the write-requested data P21, the write-requested data P21 occurs at the current time 100. Then, the flash memory controller 140 checks the block number and the previous write time to which the previous data of the data P21 requested to be written through the timestamp calculation unit 141. At this time, if the data without the previous write time, that is, the previous write time is marked as Null, the flash memory controller 140 determines the write request data P21 as cold data, and the new cold block Blk # 5 of the cold block pool The data P21 requested to be written is stored. In addition, the flash memory controller 140 allocates the data retention time as the second data retention time (Conventional Retention Time). Here, the flash memory controller 140 updates the current write time to 100 because the write-requested data P21 is an initial write.

6 is a diagram showing SSD variable values used in simulation of a flash memory control method according to an embodiment of the present invention.

In order to verify the effect of the flash memory control method according to an embodiment of the present invention, an experiment was conducted by applying an SSD patch to DiskSim, which is known as a representative storage simulator. The simulator uses input / output (I / O) traces as input values to reproduce the traces to check the response time, input / output operations per second (IOPS), and garbage collection. IOPs is a performance metric used to benchmark computer storage devices such as HDDs, SSDs and SANs. The DiskSim simulator was modified to work according to an embodiment of the present invention.

Also, the SSD specifications as shown in FIG. 6 were constructed and tested. For example, SSD specifications include SSD capacity, page / block size, page read / write latency, block erase latency, and over-provisioning rate ( Ove-provisioning ratio), size of hot block pool, data retention time (hot / cold block pool): retention time (hot / cold block pool), number of storage and deletion (hot / cold block pool) ): P / E cycles (Hot / Cold block pool) may be included. As shown in FIG. 6, 256 pages of 4 KB were configured to constitute a total of 256 GB SSD through one block. For the experiment, a workload of MSR-Cambridge, which collected I / O traces for 7 days, was used. The size of the hot block pool was set to 10% of the total SSD size, and the other areas were set to the cold block pool. In the case of the frequency-based hot / cold method, the cool down window is managed to manage 128 blocks, and in the case of the write request size method, the case of data smaller than 8 KB is determined as hot data. For example, it is assumed that the data retention time is set to one day, and if the update interval takes longer than this, a refresh operation is required.

7 is a view showing a comparison of the life of the SSD, when applying the prior art and an embodiment of the present invention.

As illustrated in FIG. 7, when a conventional Write Request Size based technique, an Update Frequency based technique and a flash memory control method according to an embodiment of the present invention are applied, each technique Let's look at the lifespan results (701, 702, 703) of the SSD. Here, the lifespan of the SSD may be expressed as a normalized lifespan.

In the flash memory control method according to an embodiment of the present invention, it can be seen that the lifetime is improved by about 5 times to a maximum of 10 times or more compared to the conventional write request size-based technique and update frequency-based technique. It can be seen that the result of this life comparison is similarly improved for various I / O traces. For example, various I / O traces include hardware monitoring (hm_1), research projects (rsrch_1, rsrch_2), source control (src2_1, src2_2), and I / O traces generated while managing the web server (web_2).

As described above, the flash memory control method according to an embodiment of the present invention uses a method of adjusting data retention time to improve life. The data retention time refers to a period during which data stored in the flash memory 144 can guarantee data integrity. Once the data retention time passes after the data is written, data loss may occur due to electronic loss of memory. When the data retention time of the flash memory 144 is shortened, the number of possible storage and deletion (P / E cycle) of the flash memory 144 increases.

Meanwhile, since hot data having a short update time interval changes data frequently in a short time, data integrity can be maintained even if the data retention time is kept short. Based on this, in the flash memory control method according to an embodiment of the present invention, data transferred from the host system to the SSD is divided into hot data and cold data, and the data retention time of the hot data is greater than the data retention time set in the cold block pool. It can be shortened to improve the lifespan of the SSD.

8 is a view showing a comparison of response time when applying the prior art and an embodiment of the present invention.

Although the flash memory control method according to an embodiment of the present invention shortens the data retention time of hot data, the response times 801, 802, and 803 between the prior art and the embodiment of the present invention are largely changed. It can be confirmed that there is no. That is, even if the retention time of the hot data is shortened, since the response time is similar, it can be confirmed that there is no difference in the performance of the SSD. Here, the response time may be expressed as a normalized response time.

On the other hand, the embodiment of the present invention can significantly increase the durability of a NAND flash memory-based SSD with a limited lifespan, which can also be utilized in a large data center environment requiring high durability of a storage device.

Systems that deal with large amounts of data often have multiple users. At this time, metadata update caused by concurrent application driving and file manipulation from a large number of users mainly consists of updating data of a fairly small size. In addition, the metadata has a feature that the update time interval is short because the file data is updated together whenever the data is updated as well as being small. Therefore, the flash memory control method can determine such metadata as hot data.

On the other hand, the backup data generated for data recording and preservation is updated due to the nature of the backup, so updates are rarely performed, so the update interval is long. Therefore, the flash memory control method may determine that these data are cold data. As such, it can be said that the distinction between such hot data and cold data is sufficiently effective even in a general use environment. Therefore, the flash memory control method according to an embodiment of the present invention can greatly improve storage durability while making full use of characteristics due to data retention time of the flash memory.

Although described above with reference to the drawings and examples, the protection scope of the present invention is not meant to be limited by the drawings or examples, and those skilled in the art will think of the present invention described in the claims below And it will be understood that various modifications and changes may be made to the present invention without departing from the scope.

10: host system
100: flash memory system
110: host interface
120: central processing unit
130: buffer memory
140: flash memory system
141: time stamp calculation unit
142: flash control
143: flash drive
144: flash memory

Claims (24)

In the flash memory control method performed by the flash memory controller,
Determining a data type as hot data or cold data according to an update time interval of write-requested data to be stored in the flash memory;
Storing the write-requested data in a hot block pool or a cold block pool provided in the flash memory according to the determined data type;
Allocating a data retention time as a first data retention time or a second data retention time according to the block pool in which the write-requested data is stored; And
Updating the write time of the stored write-requested data to the current write time,
The first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool,
In the determining of the data type, the update time interval between the previous write time of the write-requested data and the current write-request time is compared with the first data retention time to determine the data type as hot data or cold data,
In the allocating step, the first data retention time set in the hot block pool is adjusted according to a characteristic of an input / output (I / O) trace where the write requested data is generated. According to claim 1,
Checking whether a previous write time of the write-requested data is recorded; And
And if the previous write time is not recorded, determining the data type of the data requested to be written as cold data. delete According to claim 1,
The step of determining the data type,
A flash memory control method for determining that the update time interval between the previous write time of the write-requested data and the current write-request time is less than the first data retention time, as hot data. According to claim 1,
The determining by the hot data or cold data,
A flash memory control method for determining that the update time interval between the previous write time of the write-requested data and the current write-request time is equal to or greater than the first data retention time, as cold data. According to claim 1,
The step of storing the write request data,
If the previous data for the write-requested data is stored in a hot block pool or a cold block pool, the flash memory control method of invalidating the previous data stored in the block pool. delete According to claim 1,
The write-requested data whose data type is determined to be hot data,
Flash memory control method characterized in that the at least one metadata generated due to the application driving or file manipulation of the host connected through the host interface. According to claim 1,
Write-requested data whose data type is determined to be cold data,
Flash memory control method characterized in that the backup data generated by the backup operation of the host connected through the host interface. According to claim 1,
The flash memory,
A flash memory control method characterized in that it is a flash memory of any one of SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell) and QLC (Quad Level Cell). A flash drive having at least one flash memory, wherein the storage area of the flash memory is divided into a hot block pool and a cold block pool; And
The data type is determined by hot data or cold data according to the update time interval of the data requested to be written to the flash drive, and the write requested data is stored in a hot block pool or a cold block pool, and the block in which the write request data is stored And a flash memory controller that allocates data retention time according to a pool as a first data retention time or a second data retention time, and updates the write time of the stored write-requested data to the current write time,
The first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool,
The flash memory controller compares the update time interval between the previous write time of the write-requested data and the current write-request time with the first data retention time to determine a data type as hot data or cold data, and the write request Flash memory system characterized in that to adjust the first data retention time set in the hot block pool according to the characteristics of the input / output (I / O) trace where the generated data is generated. The method of claim 11,
The flash memory controller,
A flash memory system that checks whether a previous write time of the write-requested data is recorded, and if the previous write time is not recorded, determines a data type of the write-requested data as cold data. delete The method of claim 11,
The flash memory controller,
If the update time interval between the previous write time of the write-requested data and the current write-request time is less than the first data retention time, it is determined as hot data. The method of claim 11,
The flash memory controller,
If the update time interval between the previous write time of the write-requested data and the current write-request time is greater than or equal to the first data retention time, it is determined as cold data. The method of claim 11,
The flash memory controller,
If the previous data for the write-requested data is stored in a hot block pool or a cold block pool, the previous data stored in the block pool is invalidated. delete The method of claim 11,
The flash memory is a flash memory system characterized in that it is a flash memory of any one of SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell) and QLC (Quad Level Cell). A flash drive having at least one flash memory, wherein the storage area of the flash memory is divided into a hot block pool and a cold block pool;
A timestamp calculation unit managing a write time of data stored in the flash memory and calculating an update time interval of write-requested data to be stored in the flash memory; And
Data type is determined by hot data or cold data according to the calculated update time interval, and the write-requested data is stored in the hot block pool or cold block pool, and the data retention time according to the block pool in which the write-requested data is stored. And a flash control unit that allocates the first data retention time or the second data retention time,
The timestamp calculator updates the write time of the stored write-requested data to the current write time, and the first data retention time set in the hot block pool is less than the second data retention time set in the cold block pool,
The flash control unit compares the update time interval between the previous write time of the write-requested data and the current write-request time with the first data retention time to determine a data type as hot data or cold data, and the write-requested data Flash memory system characterized in that for adjusting the first data retention time set in the hot block pool according to the characteristics of the input / output (I / O) trace is generated. A method for controlling a flash memory in a flash memory system erased in units of blocks,
Data in the block unit in the flash memory controller-the data has a page unit of the flash memory, and the block consists of a plurality of pages-the time when the write is written and the written data is written comparing the updated time after (write) and classifying the data type into hot data and cold data; And
In the flash drive, based on the divided data type, comprising the step of storing the data having the same data type, and storing,
In the flash memory controller, the data retention time of the hot data is set to be shorter than the data retention time of the cold data,
The distinguishing step compares the time between the write time and the updated time interval after the written data is written with the data retention time of the hot data to compare the data type with hot data or cold data. Separated by,
Flash memory control method, characterized in that for adjusting the data retention time of the hot data according to the characteristics of the input / output (I / O) trace where the written data is generated in the flash memory controller. The method of claim 20,
The step of distinguishing,
Recording a time at which the data is written in the block unit in the flash memory controller in a mapping table; And
Comprising the step of obtaining the difference between the time the data is written (write) and the updated time in the flash memory controller and comparing with the data retention time of the set hot data,
As a result of the comparison in the comparing step, when the difference value between the updated times is smaller than the data retention time of the set hot data, it is classified as hot data, and the difference value between the updated times is the data retention time of the set hot data If the above is the flash memory control method characterized in that the classification into the cold data. The method of claim 20,
The storing step,
And storing the divided hot data in a hot block pool, which is a storage area of hot data, and storing the cold data in a cold block pool, which is a storage area of cold data. The method of claim 20,
When the ratio of the size of the storage area of the hot data is less than a predetermined value in consideration of the ratio of the size of the storage area of the hot data to the storage space of the flash drive, the size of the storage area of the hot data and the data of the hot data are maintained. Flash memory control method further comprising the step of adjusting the time. In a flash memory system that is erased in block units,
Data in the block unit-the data has a page unit of a flash memory, and the block is composed of a plurality of pages-the time when the data is written and the written data is written Then, the flash memory controller classifies the data type into hot data and cold data by comparing the updated time; And
A flash drive having at least one flash memory, and storing the data having the same data type based on the distinguished data type, is stored.
In the flash memory controller, the data retention time of the hot data is set to be shorter than the data retention time of the cold data,
The data type is divided into hot data or cold data by comparing the time at which the data is written and the updated time interval after the data is written to the data retention time of the hot data.
And adjusting the data retention time of the hot data according to the characteristics of the input / output (I / O) trace where the written data is generated.

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