KR20190061426A - Flash memory system and control method thereof - Google Patents

Abstract

According to an embodiment of the present invention, a flash memory control method comprises the steps of: determining a data type as hot data or cold data according to an update time interval of write-requested data to be stored in a flash memory; storing the write-requested data in a hot block pool or a cold block pool provided at the flash memory according to the determined data type; allocating data retention time into first data retention time or second data retention time according to the block pool storing the write-requested data; and updating write time of the stored write-requested data with 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. The present invention can increase life of an SSD provided with the flash memory.

Description

[0001] Flash memory system and control method [

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

Semiconductor memory devices are divided into volatile memory devices and non-volatile memory devices. Volatile memory devices have a fast read / write speed, but the stored contents are lost when the external power supply is interrupted. On the other hand, the nonvolatile memory device preserves its contents even if the external power supply is interrupted. Therefore, a non-volatile memory device is used to store information that should be preserved whether power is applied or not. Particularly, among nonvolatile memories, a flash memory is highly advantageous in application to a large capacity auxiliary memory device because it has a higher integration density than an existing EEPROM (Electrically Erasable Programmable Read-Only Memory).

In recent years, flash memory has been used as a storage medium to replace a hard disk drive (HDD) in accordance with technological advances and price reduction of flash memory devices. The above-described storage device is also referred to as a solid state drive or a solid state disk. Hereinafter, it will be simply referred to as an SSD. SSDs can input and output data at high speeds, but have significantly lower mechanical delays and failure rates. In addition, the SSD is advantageous in that data is not easily damaged even when an external impact is generated, and heat generation, noise, and power consumption are reduced, and the SSD can be reduced in size and weight. Thus, the demand for SSDs that do not use mechanically rotating platters is increasing rapidly with low power and high capacity mobile trends. However, SSDs based on NAND flash have a disadvantage that the number of times of writing and erasing data (P / E cycle) is limited.

As SSDs based on NAND flash memory become popular, SSDs are widely adopted as storage devices in enterprise-class data centers. NAND flash memories are used not only as personal computers but also as storage devices for enterprise-class servers based on low power and high performance. The need for SSDs based on NAND flash memory that can store large amounts of data in accordance with these trends is also increasing. For this purpose, MLC (Multi Level Cell) and TLC (Triple Level Cell) flash memory, which store 2 bits and 3 bits in one cell, have appeared. However, they have a disadvantage that their durability is greatly reduced.

On the other hand, in relation to a technique for discriminating data stored in a flash memory, conventional technologies include a write request size based method and an update frequency based method. The write request size-based scheme divides the write request data into a hot data in accordance with a size of a write request transmitted from the host to the SSD, and the cold data in a write request with a large size. In addition, the update frequency-based technique divides the data in which write operation has occurred among the recently stored data using the LRU (Least Recently Used) technique as hot data and the other data as cold data.

Korean Patent Publication No. 10-2013-0076429 (published on July 08, 2013)

However, when the hot data and the cold data are distinguished from each other as in the related art, the prior art can not fully utilize the improved durability of the flash memory. This is because, in the case of the related art, a case in which the update is not frequent even though the data of the small size write request is significant. In addition, when the LRU method is used, it is necessary to have a long data retention time even though it is divided into hot data. In the case of an SSD for storing large-scale data, MLC and TLC flash memories, which store 2 bits or 3 bits in one cell, are mainly used. However, they have the disadvantage of durability.

The embodiments of the present invention determine the data type as hot data or cold data according to the update time interval of the write-requested data, store the data type in the corresponding block pool, allocate the data retention time for each block pool, SUMMARY OF THE INVENTION The present invention provides a flash memory system and a control method thereof that can improve the lifetime of a built-in SSD.

According to an embodiment of the present invention, there is provided a method of controlling a flash memory performed by a flash memory controller, the method comprising: generating hot data or cold data according to an update time interval of write- determining a data type by a data type; Storing the write-requested data in a hot block pool or a cold block pool of the flash memory according to the determined data type; Assigning a data retention time as a first data retention time or a second data retention time according to a block pool in which the write-requested data is stored; And updating the write time of the stored write requested data to a current write time, wherein a first data hold time set in the hot block pool is less than a second data hold 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 determining the data type of the write-requested data as cold data if the previous write time is not recorded.

The step of determining the data type may further include comparing the update time interval between the previous write time of the write requested data and the current write requested time with the first data hold time to determine the data type as hot data or cold data have.

The step of discriminating the data type may be determined as hot data if the update time interval between the previous write time of the write requested data and the current write requested time is less than the first data hold time.

The step of discriminating the hot data or the cold data may be judged as the cold data if the update time interval between the previous write time of the write requested data and the current write requested time is equal to or longer than the first data hold time.

The step of storing the write-requested data may invalidate the previous data stored in the block pool if the previous data of the write-requested data is stored in the hot block pool or the cold block pool.

The allocating step may adjust a first data retention time set in the hot block pool according to characteristics of an input / output (I / O) trace in which 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 that occurs due to an application drive or file operation of the host connected through the host interface.

The write requested data whose data type is determined to be cold data may be backup data generated due to the backup operation of the host connected through the 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, there is provided 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 a controller for determining the 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 requested data in a hot block pool or a cold block pool, And a flash memory controller for allocating a data retention time as a first data retention time or a second data retention time according to a block pool and updating a write time of the stored write requested data to a current write time, The first data holding time set in the cold block pool is less than the second data holding time set in the cold block pool.

The flash memory controller may check whether the previous write time of the write-requested data is recorded. If the previous write time is not recorded, the flash memory controller may 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 requested time with the first data retention time.

The flash memory controller can determine the hot data if the update time interval between the previous write time of the write requested data and the current write requested time is less than the first data hold time.

The flash memory controller can discriminate the data as the cold data if the update time interval between the previous write time of the write requested data and the current write requested time is equal to or longer than the first data hold time.

The flash memory controller may invalidate previous data stored in the block pool if previous data of the write-requested data is stored in a hot block pool or a cold block pool.

The flash memory controller may adjust a first data retention time set in the hot block pool according to characteristics of an input / output (I / O) trace in which 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, there is provided 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 for 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 a controller for determining a data type as hot data or cold data according to the calculated update time interval, storing the write requested data in a hot block pool or a cold block pool, Wherein the time stamp calculation unit updates the write time of the stored write-requested data to a current write time, and updates the write-in time of the write-requested data to the write- 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, there is provided a method of controlling a flash memory in a flash memory system that is erased on a block basis, the method comprising the steps of: Wherein the block is composed of a plurality of pages, and comparing the time at which the write data is written with the updated time after the write data is written, thereby converting the type of the data into hot data ) And cold data (Cold Data); And storing data having the same data type in the flash drive, wherein the data retention time of the hot data in the flash memory controller is the data of the cold data The flash memory control method is set shorter than the holding time.

Wherein the dividing comprises: recording, in a block table, the time at which the data is written in the mapping table in the flash memory controller; And a step of obtaining a difference between the time at which the data is written and the updated time at the flash memory controller and comparing the data with the data retention time of the set hot data, If the difference value between the updated time is smaller than the data retention time of the set hot data, the data can be classified into the hot data, and if the difference between the updated time is the data retention time of the set hot data or more, .

The storing step may store the separated hot data in a hot block pool which is a storage area of hot data, and store the cold data in a cold block pool which is a storage area of the cold data.

The flash memory control method may further include a step of, when a ratio of a size of the storage area of the hot data to a storage area of the hot data is smaller than a predetermined value, And the data retention time of the hot data.

According to another embodiment of the present invention, there is provided a flash memory system erased on a block-by-block basis, wherein data on a block-by-block basis, the data having a page unit of a flash memory, The type of the data is divided into hot data and cold data by comparing the write time of the write data with the updated time after the write data is written, Flash memory controller; And a flash drive for storing data having the same data type on the basis of the divided data type, wherein the flash memory controller includes a data retention time ) Is set shorter than the data holding time of the cold data.

1 is a block diagram of a flash memory system according to an embodiment of the present invention.
2 is a flowchart illustrating a flash memory control method 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.
FIG. 4 is a diagram illustrating hot and cold data discrimination performed by a flash controller of a flash memory controller according to an embodiment of the present invention. Referring to FIG.
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.
6 is a diagram illustrating SSD variable values used in a simulation of a flash memory control method according to an embodiment of the present invention.
FIG. 7 is a diagram showing a comparison of life spans of SSDs when applying the prior art and one embodiment of the present invention.
FIG. 8 is a diagram illustrating a comparison of response time when applying the prior art and one embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. 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 another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

1 is a block diagram of a flash memory system according to an embodiment of the present invention.

1, a 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 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 handles the SATA physical layer (Phy Layer) and the link layer. The connection between the flash memory system 100 and the host system 10 may be performed 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,

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 necessary for the read operation and the write operation from the host interface 110. For example, when an instruction is inputted from the outside, it is stored in the host interface 110. The host interface 110 informs 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 as a single configuration, it may be composed of two or more multiprocessors. Each of the plurality of multiprocessors constituting the central processing unit 120 can divide and process the control operation. That is, the flash memory system 100 can perform multi-tasking by a plurality of multiprocessors. In addition, the flash memory system 100 including a plurality of multiprocessors can perform parallel processing. By parallel processing, the flash memory system can achieve high performance even when driven by a relatively low frequency clock. The central processing unit 120 can 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 to perform address mapping management, ware-leveling management of flash memory, Management of data preservation due to blocking, and the like. The buffer memory 130 may be 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 stored in the nonvolatile RAM or the volatile RAM.

The write-requested data can be temporarily stored in the non-volatile RAM, and is temporarily stored in the flash drive 143 after being temporarily stored. At this time, the central processing unit 120 can transmit a host command processing signal (Complete) to the host system 10 immediately after the input data is requested to write to the nonvolatile RAM.

The flash memory controller 140 processes the flash memory command and data transfer to the flash drive 143 such as read, write and erase. In addition, there is a flash memory channel for connecting the flash drive 143.

The flash drive 143 may include a plurality of NAND type flash memories 144 having a large storage capacity as a storage medium of the flash memory system 100. The flash drive 143 may be composed of a plurality of memory devices. Although a NAND flash memory has been described as an example of a storage medium, it may be composed of other nonvolatile memory devices. For example, PRAM, MRAM, ReRAM, FRAM, NOR flash memory, or the like may be used as a storage medium, and a flash memory system in which heterogeneous memory devices are mixed can be applied. And a volatile memory device (e.g., a DRAM) as a storage medium.

Meanwhile, 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. 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. On the contrary, 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 holding time set in the hot block pool as cold data. The flash memory controller 140 allocates the data retention time of the cold data to 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. The shorter the data retention time, the greater the number of cell erasures. Based on this, the flash memory controller 140 keeps the data holding time of the data (hot data) having short update intervals short. On the other hand, the flash memory controller 140 can improve the lifetime of the SSD by providing the data holding time of the long update interval data (cold data) relatively longer than the hot data.

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

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

The time stamp calculation unit 141 manages the writing time of the data stored in the flash memory 144. [ The time stamp calculation unit 141 calculates the update time interval of the 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 time stamp calculation unit 141, and stores the requested data in the hot block pool or the cold block pool. Here, the flash controller 142 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. At this time, the flash control unit 142 can determine that the data is hot data 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 hold 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 equal to or greater than the first data hold time, the flash control unit 142 can determine the data as cold data.

The flash controller 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 write-requested data is stored. Here, the first data holding time set in the hot block pool is less than the second data holding time set in the cold block pool. The flash control unit 142 records the time for writing data on a block-by-block basis through the time stamp calculation unit 141. The flash control unit 142 compares the current write time with the next write time, i.e., update time, and classifies the data type into hot data and cold data.

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 the cold block pool. The flash drive 143 stores data having the same data type based on the data type discriminated by the flash control unit 142. [ Thereafter, the flash drive 143 can provide a high write and erase count (P / E cycle) by shortening the data retention time to the first data retention time in the case of hot data.

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

On the other hand, the flash control unit 142 checks whether the previous write time of the write-requested data is recorded. If the previous write time is not recorded, the flash control unit 142 can determine the data type of the write-requested data as cold data.

The flash control unit 142 may invalidate the previous data stored in the block pool if the previous data of the write-requested data is stored in the hot block pool or the cold 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 in which the write requested data is generated. The flash control unit 142 can 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, in consideration of the ratio of the size of the storage area of the hot data to the storage space of the entire flash drive 143, if the ratio of the size of the storage area of the hot data is less than the predetermined value, Can be reduced. Alternatively, the flash control unit 142 may reduce the first data holding time allocated to 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 operation or file operation 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 data recording or data saving 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 a single level cell (SLC), a multi level cell (MLC), a triple level cell (TLC), and a quad level cell (QLC).

Hereinafter, a 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 on a block-by-block basis.

The flash memory controller 140 compares the time at which data is written in block units with the updated time since the write data is written. Here, the data has a page unit of a flash memory, and the block is composed of a plurality of pages. The flash memory controller 140 divides the data type into hot data and cold data.

The flash drive 143 has at least one flash memory 144. The flash drive 143 stores data having the same data type on the basis of the data type discriminated in the flash memory controller 140.

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 illustrating a flash memory control method 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 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 144. [ Here, the flash memory controller 140 checks whether the previous write time of the write-requested data is recorded. If it is determined that the previous write time is not recorded, the flash memory controller 140 may determine the data type of the write-requested data as the cold data.

In step S103, the flash memory controller 140 stores the data requested to be written to the hot block pool or the 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 holding time set in the hot block pool is less than the second data holding 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 issued 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 the write time of the data requested to be written by the time stamp calculation unit 141 is recorded.

If it is determined in step S203 that the write time of the write-requested data is recorded (S202), the flash memory controller 140 determines whether the update time interval of the write-requested data is shorter than the first data retention time of the hot block pool Check.

If the update time interval of the write-requested data is shorter than the first data retention time of the hot-block pool in step S204, 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 hold time, the flash memory controller 140 determines that the write data is hot data, And the update time interval between the current write request time and the first data retention time is greater than or equal to the first data retention time.

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

If the previous data of the write-requested data is stored in the block pool of the flash memory 144 in step S206, the flash memory controller 140 invalidates the previous data of the stored block pool (Invalid).

In step S207, the flash memory controller 140 stores the write-requested data in the 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 write-requested data 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 time stamp calculation unit 141 in the data block to which the newly requested write requested data belongs.

On the other hand, if it is determined in step S209 that the write time of the write-requested data is not recorded (S202), the flash memory controller 140 distinguishes the write-requested data as the initial write data and determines the data as the cold data. If the update time interval of the data requested to be written is not shorter than the first data retention time of the hot block pool (S203), the flash memory controller 140 determines the write request data as the cold data.

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

If the previous data of the write requested data is stored in the block pool of the flash memory 144 in step S211, the flash memory controller 140 invalidates the previous data of the stored block pool (Invalid).

In step S212, the flash memory controller 140 stores the write-requested data in the 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 write-requested data is stored.

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

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

The method of controlling flash memory according to another embodiment of the present invention is a method of controlling the flash memory controller 140 in such a manner that the time at which data is written in block units in the flash memory controller 140 and the updated time after the write data is written Dividing the data type into hot data and cold data and dividing the data having the same data type by the data type discriminated in the flash drive 143 . 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.

A method of controlling a flash memory according to another embodiment of the present invention includes the steps of writing data in a block table in a block unit in a flash memory controller 140 in a mapping table and writing data in a mapping table in a flash memory controller 140 and comparing the updated time with the data retention time of the hot data. Here, the flash memory controller 140 classifies the data as hot data when the difference value between the updated times is smaller than the data holding time of the hot data, and when the difference value between the updated times is equal to or longer than the data holding time of the hot data, Data.

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

FIG. 4 is a diagram illustrating hot and cold data discrimination performed by a flash controller of a flash memory controller according to an embodiment of the present invention. Referring to FIG. 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.

The embodiment of the present invention will be described in two layers of the flash controller 140 and the flash drive 143 in the SSD.

First, the flash memory controller 140 physically divides 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 hot data, and the cold block pool stores the remaining data. At this time, the hot block pool shortens the data holding time by only storing hot data, thereby raising the program / erase cycles (P / E cycle).

For such a separation, the flash control unit 142 distinguishes the data type. The flash control unit 142 records a time at which data is recorded in each block using a time measuring unit such as the time stamp calculating unit 141. [ When data to be updated is generated, 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 holding time of the hot block pool of the flash drive 143, it is divided into hot data, and otherwise, it is divided into cold data. Accordingly, the flash memory controller 140 can effectively distinguish hot and cold data, and prevent side effects such as data maintenance time and data integrity problems.

As shown in FIGS. 4 and 5, a case where the write-requested data P9 and another write-requested data P21 are generated will be described as an example.

First, it is assumed that the current time is 100. It is also 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 numerical representation of a time for convenience of explanation, and is not limited to a specific time.

Referring to the data P9 requested to be written, data update (data update) occurs at the current time 100 in the data P9 requested to be written. Then, the flash memory controller 140 confirms the block number to which the previous data of the data P9 requested to be written through the time stamp calculation unit 141 belongs and the previous write time (Blk # 2 and 85 hours). The flash memory controller 140 calculates the update time interval (100-85 = 15) between the current time 100, i.e., the write request time and the previous write time, and compares the update time interval with the first data retention time 36 (Short Retention Time = 36) And confirms that the update time interval 15 is less than the first data holding time. Then, the flash memory controller 140 determines the write-requested data P9 as hot data, invalidates the previous data P9 stored in Blk # 2 of the cold block pool, and writes the data P9 to the hot block Blk # 1 And stores the write-requested data P9. The flash memory controller 140 allocates the data retention time as the first data retention time. Here, the data P9 requested to be written is stored in the hot block pool although the previous data is stored in the cold block pool, but is determined as hot data. In this way, if the data requested to be written is stored in the hot block pool and is determined to be the cold data, it can be stored in the cold block pool. Then, the flash memory controller 140 updates the previous write time 85 of the write requested data P9 to 100, which is the current write time.

Next, referring to the write request data P21, the write request data P21 is generated at the current time 100. Then, the flash memory controller 140 checks the block number to which the previous data of the write-requested data P21 belongs and the previous write time through the timestamp calculation unit 141. [ If the previous write time is Null, the flash memory controller 140 determines the write request data P21 as the cold data and sets the new cold block Blk # 5 in the cold block pool And stores the data P21 requested to be written. Then, the flash memory controller 140 allocates the data retention time as the second data retention time. Here, the flash memory controller 140 updates the current write time to 100 because the write-requested data P21 is the initial write.

6 is a diagram illustrating SSD variable values used in a 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 SSD patch was applied to DiskSim, which is known as a typical storage device simulator, and the experiment was conducted. The simulator can check the response time, input / output operations per second (IOPS), garbage collection, etc. by using the input / output (I / O) trace as an input value. IOPs are performance measurement units used to benchmark computer storage devices such as HDDs, SSDs, and SANs. The DiskSim simulator was modified to operate in accordance with the embodiment of the present invention.

Also, the SSD specification as shown in FIG. 6 was constructed and tested. For example, SSD specifications include SSD capacity, page / block size, page read / write latency, block erase latency, and over-provisioning ratio (Hot / cold block pool), retention time (hot / cold block pool), storage and deletion times (hot / cold block pool) ): P / E cycles (hot / cold block pool). As shown in FIG. 6, 256 pages of 4 KB are set to constitute a total of 256 GB of SSD through one block. For the experiment, I used MSR-Cambridge workload that collected I / O trace for 7 days. The size of the hot block pool is set to 10% of the total SSD size, and the remaining area is set as a cold block pool. In the frequency-based hot / cold method, the cool down window manages 128 blocks. In the case of the write request size method, the data of less than 8 KB is judged as hot data. For example, it is assumed that the data retention time is set to 1 day, and a refresh operation is required when the update interval takes longer than this.

FIG. 7 is a diagram showing a comparison of life spans of SSDs when applying the prior art and one embodiment of the present invention.

As shown in FIG. 7, when a conventional write request size based method, an update frequency based method, and a flash memory control method according to an embodiment of the present invention are applied, Let's look at the life results (701, 702, 703) of the SSD. Here, the lifetime of the SSD can be expressed as a normalized lifespan.

It can be seen that the flash memory control method according to the embodiment of the present invention improves the lifespan from 5 times to 10 times or more as compared with the conventional write request size based technique and update frequency based techniques. This lifetime comparison result is similarly improved for various I / O traces. For example, various I / O traces include I / O traces generated during hardware monitoring (hm_1), research projects (rsrch_1, rsrch_2), source controls (src2_1, src2_2), and web server (web_2).

As described above, the flash memory control method according to the embodiment of the present invention uses a method of adjusting the data holding time to improve the life. The data retention time means a period during which data stored in the flash memory 144 can ensure data integrity. Once the data has been stored and the data retention time has passed, data loss may occur due to the electronic loss of the memory. If the data retention time of the flash memory 144 is shortened, the number of times of storage and deletion (P / E cycle) in the flash memory 144 increases.

On the other hand, hot data with a short update time interval can maintain data integrity even if the data retention time is kept short because the data is frequently changed in a short time. The flash memory control method according to an embodiment of the present invention divides the data transferred from the host system to the SSD into hot data and cold data and sets the data retention time of the hot data to be greater than the data retention time set in the cold block pool The life of the SSD can be shortened.

FIG. 8 is a diagram illustrating a comparison of response time when applying the prior art and one embodiment of the present invention.

Although the flash memory control method according to the embodiment of the present invention shortens the data retention time of hot data, the response time 801, 802, 803 between the prior art and the embodiment of the present invention, as shown in FIG. 8, . That is, even if the holding time of the hot data is shortened, the response time is similar, so that the performance of the SSD is not different. Here, the response time may be expressed as a normalized response time.

Meanwhile, the embodiment of the present invention can greatly enhance the durability of the NAND flash memory-based SSD having a limited life, and can be utilized in a large-scale data center environment requiring high durability of the storage device.

In a system for handling large-scale data, there are many users in many cases. At this time, metadata update caused by simultaneous application execution and file manipulation performed by many users is mainly due to data update of a small size. In addition, the meta data is characterized not only by its small size, but also by updating the file data every time the file data is updated. Therefore, the flash memory control method can determine such metadata as hot data.

On the other hand, due to the nature of the backup, the backup data generated for recording and archiving data is stored only once, and the updating time interval becomes longer. Therefore, the flash memory control method can determine such data as the cold data. Thus, even in a normal use environment, the classification of hot data and cold data is sufficiently effective. Therefore, the flash memory control method according to the embodiment of the present invention can greatly improve the storage durability while maximizing the characteristics due to the data retention time of the flash memory.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions as defined by the following claims It will be understood that various modifications and changes may be made thereto without departing from the spirit and scope of the invention.

10: Host system
100: Flash memory system
110: Host interface
120: central processing unit
130: buffer memory
140: Flash memory system
141: Timestamp calculation unit
142:
143: flash drive
144: flash memory

Claims (24)

A flash memory control method performed by a 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 of the flash memory according to the determined data type;
Assigning a data retention time as a first data retention time or a second data retention time according to a 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. The method according to claim 1,
Confirming 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 write-requested data as the cold data. The method according to claim 1,
Wherein the step of determining the data type comprises:
Comparing the update time interval between the previous write time of the write requested data and the current write requested time with the first data hold time to determine the data type as hot data or cold data. The method of claim 3,
Wherein the step of determining the data type comprises:
If the update time interval between the previous write time of the write requested data and the current write requested time is less than the first data hold time, the hot data is determined. The method of claim 3,
Wherein the step of discriminating the hot data or the cold data comprises:
If the update time interval between the previous write time of the write request data and the current write request time is equal to or longer than the first data retention time, judges the data as cold data. The method according to claim 1,
Wherein the step of storing the write-
And if the previous data of the write-requested data is stored in the hot block pool or the cold block pool, invalidates the previous data stored in the corresponding block pool. The method according to claim 1,
Wherein the assigning comprises:
And controlling a first data holding time set in the hot block pool according to a characteristic of an input / output (I / O) trace in which the write requested data is generated. The method according to claim 1,
The write-requested data, whose data type is determined as hot data,
Is at least one meta-data generated due to application activation or file manipulation of a host connected via a host interface. The method according to claim 1,
The write-requested data in which the data type is determined to be the cold data,
And backup data generated due to a backup operation of the host connected through the host interface. The method according to claim 1,
The flash memory includes:
Wherein the flash memory is a flash memory of any one of a single level cell (SLC), a multi level cell (MLC), a triple level cell (TLC), and a quad level cell (QLC). 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 of the hot data or the cold data is determined according to the update time interval of the data requested to be written to the flash drive, and the requested data is stored in the hot block pool or the cold block pool, And a flash memory controller for allocating a data retention time according to the pool as a first data retention time or a second data retention time and updating the write time of the stored write requested data to a 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. 12. The method of claim 11,
The flash memory controller includes:
And determines whether the previous write time of the write-requested data is recorded. If the previous write time is not recorded, the data type of the write-requested data is determined to be cold data. 12. The method of claim 11,
The flash memory controller includes:
Wherein the data type is determined 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 requested time with the first data hold time. 14. The method of claim 13,
The flash memory controller includes:
If the update time interval between the previous write time of the write requested data and the current write requested time is less than the first data hold time, the hot data is determined. 14. The method of claim 13,
The flash memory controller includes:
If the update time interval between the previous write time of the write request data and the current write request time is equal to or longer than the first data retention time, the flash memory system determines the cold data. 12. The method of claim 11,
The flash memory controller includes:
And if the previous data for the write-requested data is stored in the hot block pool or the cold block pool, invalidates the previous data stored in the block pool. 12. The method of claim 11,
The flash memory controller includes:
And controls the first data retention time set in the hot block pool according to characteristics of an input / output (I / O) trace in which the write requested data is generated. 12. The method of claim 11,
Wherein the flash memory is a flash memory of any one of a single level cell (SLC), a multi level cell (MLC), a triple level cell (TLC), and a quad level cell (QLC). 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 for 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
Wherein the controller determines the data type as hot data or cold data according to the calculated update time interval, stores the data requested to be written in the hot block pool or the cold block pool, To a first data holding time or a second data holding time,
Wherein the time stamp calculation unit updates the write time of the stored write requested data to the current write time and the first data hold time set in the hot block pool is less than the second data hold time set in the cold block pool. Flash memory system. A flash memory control method in a flash memory system erased in block units,
Wherein the data in the block unit in a flash memory controller has a page unit of a flash memory and the block is composed of a plurality of pages and a time when the write data is written comparing the updated time since the data was written and dividing the data type into hot data and cold data; And
And storing the data having the same data type in the flash drive separately from each other based on the separated data type,
Wherein the data retention time of the hot data is shorter than the data retention time of the cold data in the flash memory controller. 21. The method of claim 20,
Wherein the distinguishing step comprises:
Writing in the mapping table the time at which the data is written in the block unit in the flash memory controller; And
Determining a difference between a time at which the data is written in the flash memory controller and the updated time, and comparing the updated data with a data retention time of the set hot data,
And if the difference value between the updated time is less than the data retention time of the set hot data, the difference data is classified into hot data, The flash memory is classified into the cold data. 21. The method of claim 20,
Wherein the storing step comprises:
Storing the separated 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 the cold data. 21. The method of claim 20,
The size of the storage area of the hot data and the size of the storage area of the hot data when the ratio of the size of the storage area of the hot data to the storage area of the flash drive is less than a predetermined value, Further comprising the step of adjusting the time. In a flash memory system erased in units of blocks,
Wherein data is written in units of blocks, the data having a page unit of a flash memory, the block being composed of a plurality of pages, and a write- A flash memory controller for comparing the updated time with the hot data and the cold data by dividing the data type into hot data and cold data; And
And a flash drive having at least one flash memory and storing the data having the same data type separately based on the separated data type,
Wherein the data retention time of the hot data is shorter than the data retention time of the cold data in the flash memory controller.

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