JP2013061791A - Storage controller, storage device, and write caching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a write caching size corresponding to an exhaustion degree of a backup power supply.SOLUTION: A data buffer stores data transferred from a host device. Discharge capacity detection means detects a discharge capacity of a backup power supply charged by power supplied from a main power supply. Time calculation means calculates a first time in which write caching can be performed with power supply from the backup power supply on the basis of the detected discharge capacity, and also calculates a second time required for writing data which is stored in the data buffer and is unwritten in a medium, in the medium. Determination means determines whether it is possible to write the unwritten data in the medium within the first time on the basis of the first time and the second time, and when it is possible to write the unwritten data in the medium within the first time, transmits a response indicating writing completion to the host device. A media controller writes the unwritten data stored in the data buffer in the medium after the response indicating writing completion is transmitted.

Description

  Embodiments described herein relate generally to a storage controller, a storage apparatus, and a write caching method that write data stored in a data buffer and then write the data stored in the data buffer to a medium.

  Generally, a storage apparatus includes a medium such as a memory or a disk, and a storage controller that controls access to the medium. The storage controller generally includes a data buffer for temporarily storing data transferred from the host (host device) in order to efficiently write data to the medium.

  The storage controller stores the write data transferred from the host in the data buffer. Thereafter, the storage controller writes the data stored in the data buffer to the medium.

  Here, it is assumed that the power supply for the storage apparatus (hereinafter referred to as main power supply) is shut off while the storage controller is writing data to the data buffer. In this case, data stored in the data buffer and not written to the medium (hereinafter referred to as unwritten data in the data buffer) is lost.

  Therefore, in order to prevent the unwritten data in the data buffer from being lost when the main power supply is shut off, the storage apparatus includes a backup power supply such as a capacitor. The backup power source is charged with power supplied from the main power source.

  When the media controller writes unwritten data in the data buffer to the media, the time required to write all the unwritten data to the media (hereinafter referred to as total media write time) exceeds a predetermined time. It is determined whether or not. Even if the main power supply is shut off, this predetermined time is a time during which operation is guaranteed by supplying power from the backup power supply, and is a time during which unwritten data in the data buffer can be held in the data buffer. is there.

  If the total media write time is less than the predetermined time, the media controller notifies the host of the completion of writing, and then writes all unwritten data in the data buffer to the media. This series of operations is called write caching. On the other hand, if the total media write time exceeds the predetermined time, the media controller sends unwritten data in the data buffer to the media without notifying the host of the write completion. Write. When this media write operation proceeds and the size of the unwritten data remaining in the data buffer is reduced, and the total media write time can be secured, the media controller executes write caching.

JP-A-4-287108

  In the prior art, the predetermined time is guaranteed as the operable time when the main power supply is shut off, because the voltage of the backup power supply exceeds the predetermined voltage. However, the voltage (for example, charging voltage) of the backup power supply does not necessarily correspond to the operable time. The factor is the degree of exhaustion of the backup power supply.

  For this reason, in the prior art, the predetermined time is set in accordance with a backup power source having a high degree of fatigue. In this case, the size of data that can be written to the medium by write caching (hereinafter referred to as the write cache size) is shortened when the main power supply is shut off. That is, the write cache size is limited to a size based on the state where the backup power supply is exhausted.

  An object of the present invention is to provide a storage controller, a storage apparatus, and a write caching method capable of setting a write cache size suitable for the degree of exhaustion of a backup power supply.

  According to the embodiment, the storage controller includes a data buffer, a discharge capacity detection unit, a time calculation unit, a determination unit, and a media controller. The data buffer stores data transferred from the host device in response to a write command transmitted from the host device and instructing to write data to a nonvolatile medium. The discharge capacity detecting means detects a discharge capacity of a backup power source that is charged by power supplied from a main power source. The backup power supply backs up the main power supply when the voltage of the main power supply drops below a specified voltage. The time calculation means calculates a first time during which write caching can be performed by supplying power from the backup power source based on the detected discharge capacity. The time calculation means further calculates a second time required to write the unwritten data to the medium based on the size of the data stored in the data buffer and not written to the medium. The determination unit determines whether the unwritten data can be written to the medium within the first time by comparing the first time and the second time. If writing is possible, the determination means transmits a write completion response to the host. After the write completion response is transmitted, the media controller writes the unwritten data stored in the data buffer to the media.

1 is a block diagram showing a typical configuration of an electronic device according to an embodiment. 6 is a sequence chart for explaining write caching by control of a storage controller applied in the embodiment. 6 is a flowchart for explaining a typical procedure of write caching determination processing applied in the embodiment.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a block diagram showing a typical configuration of an electronic apparatus according to one embodiment. The electronic apparatus shown in FIG. 1 includes a storage device 10 and a host device (host) 20 that uses the storage device 10. In the present embodiment, the electronic device is a personal computer. However, the electronic device need not be a personal computer, and may be an electronic device other than a personal computer, such as a video camera, a music player, a portable terminal, a cellular phone, or a printer device. The host 20 is connected to the storage apparatus 10 via the host interface 21.

  The storage device 10 includes a medium 100 and a storage controller 110. The medium 100 is a rewritable nonvolatile storage medium used to store data. In the present embodiment, it is assumed that the medium 100 is a non-volatile memory typified by a flash memory, and the storage device 10 is a solid state drive (SSD). However, the medium 100 may be a magnetic disk, for example, and the storage device 10 may be a hard disk drive (HDD).

  The storage controller 110 controls access to the medium 100 in response to a request from the host 20. The storage controller 110 includes a host interface controller 111, a data buffer 112, a media controller 113, a capacitor 114, and a buffer controller 115. The host interface controller 111, data buffer 112, media controller 113, capacitor 114, buffer controller 115, and media 100 are interconnected by an internal bus 120.

  The host interface controller 111 communicates with the host 20 via the host interface 21. The data buffer 112 is used to temporarily store data (write data) received from the host 20. The data buffer 112 is also used for temporarily storing data read from the medium 100 (read data). The media controller 113 accesses the medium 100 in response to a request from a write control unit 117 (described later) in the buffer controller 115.

  The capacitor 114 backs up the main power supply when the voltage of the main power supply for the storage apparatus 10 falls below a specified voltage, and temporarily stores the data in the element group including the data buffer 112 and the medium 100 in the storage apparatus 10. This is a backup power source used to supply power to the power source. As an example in which the voltage of the main power supply is lower than a specified voltage, there is a case where the main power supply is cut off. In the following description, for the sake of simplicity, it is assumed that the main power supply is shut off. The capacitor 114 (that is, the backup power source) is charged by the electric power supplied from the main power source in a normal state. The main power source is, for example, an AC-DC power source.

  The capacitor 114 is, for example, an electric double layer capacitor. However, the capacitor 114 does not have to be an electric double layer capacitor. Further, a secondary battery such as a lithium ion battery may be used instead of the capacitor 114. That is, a secondary battery may be used as a backup power source. Further, the capacitor 114 may be provided outside the storage controller 110.

  The buffer controller 115 controls the data buffer 112 in response to a request for access to the medium 100 from the host 20. The buffer controller 115 includes a read control unit 116, a write control unit 117, a write caching determination unit 118, and a capacitor discharge capacity detection unit 119.

  The read control unit 116 controls reading of data from the data buffer 112. The write control unit 117 controls data writing to the data buffer 112. The write control unit 117 manages data written (stored) in the data buffer 112 using a known buffer management table (not shown). The buffer management table is held in a memory such as a DRAM. The buffer management table holds information indicating a correspondence between a buffer address indicating the position in the data buffer 112 of the data stored in the data buffer 112 and, for example, a logical address to which the data is to be written. The buffer management table also holds information indicating whether the data stored in the data buffer 112 has not been written to the medium 100. The buffer management table further holds information indicating the size (data size) of the entire data stored in the data buffer 112 and not written to the medium 100.

  The write caching determination unit 118 includes a time calculation unit 118a. The time calculation unit 118a uses the discharge capacity (mAh) of the capacitor 114 (more specifically, the discharge capacity of the capacitor 114 and the power per unit time required for the write caching) TIMEd Is calculated. Capacitor driveable time TIMEd indicates a time during which write caching can be performed by supplying power from the capacitor 114 when the main power supply is shut off. In other words, the capacitor driveable time TIMEd is stored in the data buffer 112 and unwritten data in the medium 100 (that is, unwritten data in the data buffer 112) is held in the data buffer even when the main power supply is shut off. It is time that is guaranteed to do. If unwritten data in the data buffer can be written to the medium 100 within the capacitor driveable time TIMEd, there is no possibility that the unwritten data will be lost even if the main power supply is shut off.

  The time calculation unit 118a also calculates the total media write time (second time) TIMEtotal required to write all unwritten data in the data buffer 112 to the medium 100 based on the size SIZEtotal of the unwritten data. . Note that the time calculation unit 118a may be provided independently of the write caching determination unit 118.

  The write caching determination unit 118 compares the total media write time TIMEtotal with the capacitor driveable time TIMEd. Based on the result of this comparison, the write caching determination unit 118 determines whether or not write caching for unwritten data whose data size is SIZEtotal can be executed regardless of whether or not the main power supply is shut off.

  The capacitor discharge capacity detector 119 detects the discharge capacity of the capacitor 114. The discharge capacity of the capacitor 114 represents the amount of electricity that can be supplied from the capacitor 114 by the discharge of the capacitor 114. Various methods for detecting the discharge capacity of the capacitor 114 are conventionally known. In the present embodiment, the capacitor discharge capacity detector 119 detects the discharge capacity of the capacitor 114 as follows. First, the capacitor discharge capacity detector 119 fully discharges the capacitor 114 and then fully charges the capacitor 114. The capacitor discharge capacity detector 119 measures the time (charge time) required to fully charge the capacitor 114. The charging time of the capacitor 114 corresponds to the discharge capacity of the capacitor 114. Therefore, the capacitor discharge capacity detection unit 119 refers to a table that associates the charge time with the discharge capacity of the capacitor 114 for each charge time of the capacitor 114, so that the capacitor 114 associated with the measured charge time is obtained. The discharge capacity of is detected.

  It is also possible to detect the discharge capacity of the capacitor 114 by another known method. For example, when the minimum guaranteed voltage of the capacitor 114 is determined, the capacitor discharge capacity detection unit 119 discharges the capacitor 114 to the minimum guaranteed voltage, and then fully charges the capacitor 114, and charging required for the full charge. Time may be measured. Also in this case, the capacitor discharge capacity detection unit 119 is associated with the measured charging time by referring to a table in which the charging time and the discharging capacity of the capacitor 114 are associated with each charging time of the capacitor 114. The discharge capacity of the capacitor 114 can be detected.

Next, write caching by the control of the storage controller 110 applied in this embodiment will be described with reference to the sequence chart of FIG.
First, it is assumed that the host 20 transmits a write command (hereinafter referred to as a write request) instructing to write data to the medium 100 to the storage controller 110 of the storage apparatus 10 via the host interface 21 ( Step 201). This write request includes information indicating the size (transfer size) of write data requested by the host 20 and a logical address. In the present embodiment, the host interface 21 is a serial ATA (SATA) or a serial attached SCSI (SAS) adopted in a general storage apparatus represented by an SSD or an HDD. When the host interface 21 is SATA or SAS, the host 20 transmits a write request including the transfer size to the storage controller 110 before transmitting (transferring) the write data as described above.

  When receiving the write request transferred from the host 20, the host interface controller 111 of the storage controller 110 inquires the write control unit 117 of the buffer controller 115 about the size of receivable write data (step 202). The size of write data that can be received represents the size of write data that can be written to the data buffer 112 (writeable size).

  The write control unit 117 detects the size of the free area of the data buffer 112 in response to the inquiry from the host interface controller 111 (step 203). The write control unit 117 notifies the detected size to the host interface controller 111 as the size of data that is permitted to be written from the host 20 (write permission size) (step 204). Then, the host interface controller 111 notifies the host 20 of write permission (step 205). This write permission includes information indicating the write permission size (that is, the size of data permitted to be transferred from the host 20).

  When the host 20 receives the write permission notified from the host interface controller 111, the host 20 transmits (transfers) write data of a size permitted by the write permission to the data buffer 112 via the host interface 21 and the host interface controller 111. (Step 206). When the host interface 21 is SATA or SAS as in the present embodiment, the host 20 may divide and transmit the write data of the permitted size.

  The data buffer 112 stores the write data transmitted from the host 20 in an empty area of the data buffer 112. When the data buffer 112 has received (stored) the write data of the permitted size from the host 20, the data buffer 112 notifies the write control unit 117 of the completion of data reception (step 207). In response to this data reception completion notification, the write control unit 117 notifies the write caching determination unit 118 of the size of the write data received by the data buffer 112 as the data size SIZEtotal (step 208). In this embodiment, the data size SIZEtotal notified in step 208 matches the size of the write data stored in the data buffer 112 and not yet written on the medium 100.

  On the other hand, the capacitor discharge capacity detector 119 detects the discharge capacity of the capacitor 114 asynchronously with the write operation in response to the write request from the host 20. In the present embodiment, the capacitor discharge capacity detection unit 119 detects the discharge capacity of the capacitor 114 at a predetermined timing. In this embodiment, this predetermined timing arrives at a fixed time once a day. However, the timing at which the capacitor discharge capacity detector 119 detects the discharge capacity of the capacitor 114 may be another timing. When the capacitor discharge capacity detection unit 119 detects the discharge capacity of the capacitor 114, the capacitor discharge capacity detection unit 119 notifies the detected capacitance (capacitor capacitance) to the write caching determination unit 118 (step 221).

  The time calculation unit 118a of the write caching determination unit 118 calculates the capacitor drivable time TIMEd based on the discharge capacity of the capacitor 114 notified from the capacitor discharge capacity detection unit 119 (step 222). Capacitor driveable time TIMEd indicates a time during which write caching can be performed by supplying power from the capacitor 114 when the main power supply is shut off. In the present embodiment, the time calculation unit 118a calculates the capacitor drivable time TIMEd by dividing the discharge capacity of the capacitor 114 by the current consumed by write caching.

  The capacitor driveable time TIMEd corresponds to the size of data that can be written from the data buffer 112 to the medium 100 by write caching even when the main power supply is cut off, that is, the write cache size that allows write caching. Therefore, the time calculation unit 118a calculating the capacitor driveable time TIMEd is equivalent to calculating the write cache size.

  Now, with the time calculation unit 118a of the write caching determination unit 118 already calculating the latest capacitor driveable time TIMEd, as described above, the write control unit 117 sends the data to the write caching determination unit 118. It is assumed that the size SIZEtotal has been notified (step 208). Then, the write caching determination unit 118 determines whether or not the write caching for the notified write data of the data size SIZEtotal can be executed within the capacitor driveable time TIMEd (step 209). That is, can the write caching discriminating unit 118 write the write data of the data size SIZEtotal from the data buffer 112 to the medium 100 with the power supplied from the capacitor 114 even if the main power supply is cut off? Is determined. A specific procedure of this determination processing (hereinafter referred to as write caching determination processing) will be described later.

  If it is determined in step 209 that write caching is possible, the write caching determination unit 118 transmits a write completion response to the host 20 via the host interface controller 111 as a response to the write request from the host 20. To do. Then, the media controller 113 writes the write data received (stored) by the data buffer 112, that is, the write data of the data size SIZEtotal notified from the write control unit 117 to the write caching determination unit 118 to the medium 100. The operation when it is determined in step 209 that write caching is possible is omitted in the sequence chart of FIG.

  In this embodiment, it is assumed that it is determined in step 209 that write caching is not possible. In this case, the write caching determination unit 118 sends a write completion response to the host 20 even though all the write data specified by the write request from the host 20 is stored in the data buffer 112. Deter. The reason is that if the main power supply is cut off, it is difficult to execute write caching for the notified write data of the data size SIZEtotal within the capacitor driveable time TIMEd, and at least a part of the write data is stored. This is because it may be lost.

  On the other hand, if it is determined in step 209 that write caching is not possible, the write control unit 117 writes a write data stored in the data buffer 112 and not written in the medium 100 to the medium 100. A write request is issued to 113 (step 210). In response to a write request from the write control unit 117, the media controller 113 executes the first media write operation (step 211) for writing the unwritten write data to the medium 100 at least once. This first media write operation (step 211) is executed as follows.

  First, the media controller 113 issues a data transfer request to the data buffer 112 (step 211a). In response to this data transfer request, data having a size SIZE unit in a write unit (media write unit) unique to the medium 100 is transferred from the data buffer 112 to the medium 100. The media write unit is the size of data that can be written to the medium 100 by one access. That is, data write to the medium 100 is executed in units of media write whose data size is SIZE unit.

  Data transferred from the data buffer 112 to the medium 100 and having a data size of SIZE unit is stored in the data buffer 112 and the most recently notified write data of the data size SIZEtotal (that is, unwritten to the medium 100) Write data). The media controller 113 writes the write data transferred from the data buffer 112 to the medium 100 (step 211b).

Then, the medium 100 returns a response indicating completion of writing of the data of the write unit size to the media controller 113 (step 211c). In accordance with the response from the medium 100, the media controller 113 sets the following formula so that the data size SIZEtotal is reduced by the media write unit SIZEunit.
SIZEtotal = SIZEtotal-SIZEunit (1)
Then, the data size SIZEtotal is updated. The updated data size SIZEtotal indicates the size of write data that has been stored in the data buffer 112 at the time when the latest media write is completed and has not been written to the medium 100. The media controller 113 notifies the updated latest data size SIZEtotal to the write caching determination unit 118 (step 211d).

  Then, as in the case where the data size SIZEtotal is notified from the write control unit 117, the write caching determination unit 118 determines whether or not write caching is possible based on the latest data size SIZEtotal notified from the media controller 113 (step 209). . That is, the write caching determination unit 118 determines whether or not the write caching for the write data of the latest data size SIZEtotal notified from the media controller 113 can be executed within the capacitor driveable time TIMEd. If write caching is not possible, the first media write operation (step 211) described above is executed again. Thus, the first media write operation is repeated until it is determined that write caching is possible.

  Assume that it is determined in step 209 that write caching is possible. Therefore, the write caching determination unit 118 transmits a write completion response as a response to the write request from the host 20 to the host 20 via the host interface controller 111 (step 212). Then, the media controller 113 executes at least one second media write operation (step 213) for writing the write data stored in the data buffer 112 and not written in the media 100 to the media 100. This second media write operation (step 213) is executed as follows.

  First, the media controller 113 issues a data transfer request to the data buffer 112 as in step 211a (step 213a). In response to this data transfer request, data of size SIZE unit is transferred from the data buffer 112 to the medium 100. Data having a data size of SIZE unit transferred to the medium 100 is write data that is stored in the data buffer 112 and has not been written to the medium 100. The media controller 113 writes the write data transferred from the data buffer 112 to the medium 100 as in step 211b (step 213b).

  Then, the medium 100 returns a response indicating completion of writing of the data of the write unit size to the media controller 113 (step 213c). Thereby, one second write operation (step 213) is completed. The second write operation is repeated until all the write data that is stored in the data buffer 112 and has not been written to the medium 100 is written to the medium 100. Even if the main power supply is cut off while the second write operation is repeated, all write data stored in the data buffer 112 and not yet written to the medium 100 are written to the medium 100 at that time. It is guaranteed that you can.

  Eventually, it is assumed that the data of the write unit size including the last unwritten data remaining in the data buffer 112 is written to the medium 100 (step 214). Then, the medium 100 returns a response indicating the completion of writing of the data of the write unit size to the media controller 113 in the same manner as in step 213c (step 215). Upon receiving this response, the media controller 113 notifies the write control unit 117 of the completion of media writing indicating that all unwritten data in the data buffer 112 has been written to the media 100 (step 216). Thereby, the write process corresponding to the write request from the host 20 is completed.

Next, a typical procedure of the write caching determination process executed in step 209 will be described with reference to the flowchart of FIG.
First, the write caching determination unit 118 receives the data size SIZEtotal notified from the write control unit 117 (step 301). When the first write caching determination process is executed when the data buffer 112 receives (stores) the write data transferred from the host 20, the data size SIZEtotal received in step 301 is received by the data buffer 112. Represents the size of the written data.

The time calculation unit 118a of the write caching determination unit 118 divides the data size SIZEtotal by the data size SIZEunit in units of media write (step 302). That is, the time calculation unit 118a has the following formula:
SIZEtotal ÷ SIZEunit = N + α (2)
The division indicated by is executed. Here, N is a natural number. On the other hand, α is a fraction and is zero or decimal (0 ≦ α <1).

  By the above division, the time calculation unit 118a calculates the number of media writes required to write all the write data whose data size is SIZEtotal stored in the data buffer 112 and not written to the medium 100 to the medium 100. . Here, the number of media writes is N when α is zero, that is, when “SIZEtotal” is divisible by “SIZEunit”. On the other hand, when α is non-zero, that is, when N × SIZE unit <SIZEtotal <(N + 1) × SIZE unit because “SIZEtotal” cannot be divided by “SIZEunit”, the number of media writes is N + 1.

  The time calculation unit 118a determines whether α is non-zero (α ≠ 0) based on the division result in step 302 (step 303). If α is non-zero (α ≠ 0) (Yes in Step 303), that is, if the number of media writes is N + 1, the write caching determination unit 118 proceeds to Step 304.

  In step 304, the time calculation unit 118a calculates a time β required to process data of a size “SIZEtotal−N × SIZEunit” that is less than the media write unit into the size of the media write unit. In the storage apparatus 10, data with an error correction code is generally written to the medium 100. For this reason, when writing data to the medium 100, it is necessary to align the data size with the media write unit.

  Therefore, when write data having a size less than the media write unit as described above is forcibly written to the medium 100 when the main power supply is shut off, for example, the data is determined in advance as data having a size insufficient for the media write unit. The dummy data (for example, invalid data) is used. Thus, an error correction code is generated based on the write data supplemented with dummy data. Then, the generated write data with the error correction code is written to the medium 100. In step 304, the time β required to process (process) such data is calculated.

When the time calculation unit 118a calculates the time β, the total media write time TIMEtotal required to write all the data having the data size SIZEtotal stored in the data buffer 112 and not written to the medium 100 to the medium 100 is calculated as follows: Next formula
TIMEtotal = (N + 1) x TIMEunit + β (3)
(Step 305). Here, “TIMEunit” indicates the time required to write data to the medium 100 in media write units. That is, the time calculation unit 118a calculates the total media write time TIMEtotal based on the media write count N + 1, the time TIMEunit, and the time β.

On the other hand, if α is not non-zero (α ≠ 0) (No in step 303), that is, if α is zero and the number of media writes is N, the time calculation unit 118a proceeds to step 306. In step 306, the time calculation unit 118a calculates the total media write time TIMEtotal by the following formula.
TIMEtotal = N × TIMEunit (4)
Calculate according to

  As described above, when the first write caching determination process is executed when the data buffer 112 receives the write data transferred from the host 20, the data size SIZEtotal used in the first write caching determination process is executed. Represents the size of the write data received by the data buffer 112. In this case, the total media write time TIMEtotal calculated in step 305 or 306 indicates the time required to write all the write data received (stored) by the data buffer 112 to the medium 100. Further, when the n-th (n is an integer greater than 1) write-caching determination process is executed, the data size SIZEtotal used in the n-th write-caching determination process is executed n-1 times for the write operation in step 211. Immediately after, the size of the write data stored in the data buffer 112 and not yet written to the storage controller 110 is shown.

  When the total media write time TIMEtotal is calculated by the time calculation unit 118a (step 305 or 306), the write caching determination unit 118 compares the total media write time TIMEtotal with the latest capacitor driveable time TIMEd (step 307). The capacitor drivable time TIMEd is calculated in step S222 based on the latest discharge capacity of the capacitor 114 notified from the capacitor discharge capacity detector 119.

  The write caching determination unit 118 determines whether or not write caching is possible based on the comparison result in step 307 (step 308). Here, if the total media write time TIMEtotal is equal to or shorter than the capacitor driveable time TIMEd (TIMEtotal ≦ TIMEd), the write caching determination unit 118 determines that write caching is possible. On the other hand, if the total media write time TIMEtotal exceeds the capacitor driveable time TIMEd (TIMEtotal> TIMEd), the write caching determination unit 118 cannot perform write caching for at least some unwritten data. Determine that there is. Note that even when the total media write time TIMEtotal is equal to the capacitor driveable time, the write caching determination unit 118 may determine that write caching is not possible. When it is determined in step 308 whether write caching is possible, the write caching determination process (step 209) ends.

  When it is determined that write caching is possible, write caching is executed as described above. That is, a write completion response is transmitted from the write caching discriminating unit 118 to the host 20 (step 212), and then a second media write operation for writing unwritten data in the data buffer 112 to the medium 100 (step 213). ) Is executed.

  The capacitor driveable time TIMEd applied in the present embodiment corresponds to the “predetermined time” in the prior art. However, the “predetermined time” in the prior art is a fixed time set in advance on the basis of the state where the backup power supply is exhausted. For this reason, in the prior art, the write cache size that greatly affects the write performance of the storage device is limited to the discharge capacity when the capacitor is exhausted.

  In contrast, in the present embodiment, the capacitor driveable time TIMEd is calculated based on the latest discharge capacity of the capacitor 114 detected by the capacitor discharge capacity detection unit 119. The discharge capacity of the capacitor 114 when the capacitor 114 is not exhausted is larger than that when the capacitor 114 is exhausted. That is, the discharge capacity of the capacitor 114 corresponds to the degree of exhaustion of the capacitor 114. The write cache size corresponds to the capacitor driveable time TIMEd, and increases as the capacitor driveable time TIMEd increases. As described above, in this embodiment, the write cache size suitable for the exhaustion degree of the capacitor 114 can be dynamically set based on the latest discharge capacity of the capacitor 114. Therefore, according to the present embodiment, when the capacitor 114 is not exhausted, the storage controller 110 promptly sends a write completion response to the host 20 as compared with the capacitor 114 being exhausted. The write performance of the storage apparatus 10 can be improved.

  In the above embodiment, it is assumed that a single host 20 is connected to the storage apparatus 10. However, a plurality of hosts including the host 20 may be connected to the storage apparatus 10.

According to at least one embodiment described above, it is possible to provide a storage controller, a storage device, and a write caching method that can set a write cache size that is suitable for the degree of exhaustion of a backup power supply. "
Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Storage device, 20 ... Host (host device), 100 ... Media, 110 ... Storage controller, 111 ... Host interface controller, 112 ... Data buffer, 113 ... Media controller, 114 ... Capacitor (backup power supply), 115 ... Buffer controller 117: Write control unit 118: Write caching discrimination unit 118a Time calculation unit 119 Capacitor discharge capacity detection unit

Claims (7)

A data buffer for storing data transferred from the host device in response to a write command transmitted from the host device and instructing to write data to a nonvolatile medium;
A backup power source charged by power supplied from the main power source, and a discharge capacity detecting means for detecting a discharge capacity of the backup power source that backs up the main power source when the voltage of the main power source falls below a specified voltage; ,
Based on the detected discharge capacity, a first time during which write caching can be performed by supplying power from the backup power supply is calculated, and the size of the data stored in the data buffer and not yet written to the medium A time calculating means for calculating a second time required to write the unwritten data to the medium, based on:
By comparing the first time and the second time, it is determined whether the unwritten data can be written to the medium within the first time. Determining means for transmitting a write completion response to the host;
A storage controller comprising: a media controller that writes the unwritten data stored in the data buffer to the medium after the write completion response is transmitted. If it is determined that the writing is impossible, the determination unit suppresses transmission of the write completion response to the host;
If it is determined that the writing is impossible, the media controller writes the unwritten data stored in the data buffer to the medium in units of a predetermined size, and stores the data of the predetermined size. Each time the medium is written, the time calculation means is notified of the size of unwritten data remaining in the data buffer,
The storage controller according to claim 1, wherein the time calculation unit calculates the second time again based on the notified size.   The time calculating means, assuming that N is a natural number, if the notified size is larger than N times the predetermined size and smaller than N + 1 times the predetermined size, The processing time required to process the included data less than the predetermined size into the predetermined size is calculated, and the calculated processing time is calculated N + 1 times for the predetermined size on the medium. The storage controller according to claim 2, wherein the second time is calculated by adding to a time required for writing data.   The storage controller according to claim 1, wherein the medium is a rewritable nonvolatile memory.   The storage controller according to claim 1, wherein the discharge capacity detection unit detects the discharge capacity asynchronously with a write operation corresponding to the write request. Rewritable non-volatile media,
A storage apparatus comprising: the storage controller according to claim 1, wherein access to the medium is controlled in response to a request from a host apparatus. Write caching applied to a storage controller having a data buffer for storing data transferred from the host device in response to a write command sent from the host device to write data to a non-volatile medium A method,
Detect the discharge capacity of the backup power source charged by the power supplied from the main power source,
Based on the detected discharge capacity, a first time during which write caching can be performed by supplying power from the backup power source is calculated,
Calculating a second time required to write the unwritten data to the medium based on the size of the data stored in the data buffer and not yet written to the medium;
By comparing the first time and the second time, it is determined whether it is possible to write the unwritten data to the medium within the first time,
If write is possible, a write completion response is sent to the host,
A write caching method for writing the unwritten data stored in the data buffer to the medium after the write completion response is transmitted.

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