Method for backing up power supply of disk array device and system thereof

A disk array device having two or more disk units, each disk unit including at least one disk drive, at least either of said disk units having parity bits carrying data recovery information, comprises at least one backup battery provided for each of said disk unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priorities upon Japanese Patent Application No. 2002-128591 filed on Apr. 30, 2002 and Japanese Patent Application No. 2002-278902 filed on Sep. 25, 2002, which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a method for backing up a power supply of a disk array device and a system therefor.

2. Description of the Related Art

A disk array device has now come to be in use not only in a conventional machine room of stabilized condition but also in an ordinary office environment which may sometimes suffer continuing or instantaneous power failure and the like. In particular, as the disk array device is becoming more available through downsizing and employment of open architecture in CPU, the above situation is being spread. A typical configuration of power supply in a current disk array device is illustrated inFIG. 12for example.

A disk controller11(DKU) of the disk array device10includes an error correction group15having a disk unit13comprising one or more disk drives12, and a disk unit14for parity bits containing data recovery information for the disk unit13. The disk unit13is referred to as a hard disk platter (HDD-PL) inFIG. 12, which is hereinafter simply referred to as a “platter.”

A DC-DC converter16is connected to the error correction group15including the plurality of platters to supply DC power output from an AC/DC converter18converting two systems of AC power17into DC power respectively. In this power supply system, a backup battery19is connected to the DC-DC converter16. When either of the two AC systems fails, the backup battery19supplies power to the DC-DC converter16so as to allow the disk device to operate normally until AC power restoration.

According to nature of the disk array device, it is basic requirement to improve its availability. In this context, fault tolerance design has been introduced for hardware failure in the disk device. However, such design policy has not been fully applied to power supply for the disk array device. For example, in the above-mentioned conventional power supply system, failure of AC power is able to be backed-up by the batteries, but when the batteries themselves become inoperative due to such as failure, back up of power supply is not to be expected.

Performance of the back-up batteries is generally likely to be dependent on environmental factors such as temperature, vibration, and deterioration with time. Thus, it becomes impossible to provide sufficient power backup since the performance of the batteries is insufficient. One solution for the problem will be improvement in availability of the batteries by adopting full redundant system to the backup batteries. However, such redundant system will substantially increase initial and running costs and also cause a problem of where to equip the batteries.

Next, discussion will be given for each platter. As shown inFIG. 13, a disk array device which is also called a storage device or a disk subsystem, constituting a single platter typically comprises a disk controller and a disk drive. The disk controller receives request for data transfer from a host apparatus and perform data receiving and transmission. The disk drive including a hard disk drive (HDD) writes and reads data to/from the HDD under control of the disk controller. Additional drive is able to be provided if required to enlarge storage capacity of the disk array device.

Turning now to the disk controller, as shown inFIG. 13, the disk controller comprises a host interface control logic section, a cache memory, an interface control logic section of the HDD, power supply, and a power supply monitoring section. The host interface control logic section takes charge of interfacing between an upper or a host apparatus and perform processes such as accepting request for data transfer. The cache memory provides a temporary storage for data to be written in the disk drive which has been transferred from the host apparatus. The interface control logic section provides an interface with respect to data receiving/transmission between the HDD, i.e., writing/reading of the data to/from the HDD. The power supply generates predetermined DC output from AC input AC1independently prepared for the disk controller, and supplies operating power to the host interface control logic section, a cache memory, and an interface control logic section of the HDD. See Japanese Patent Application Laid-open Publication No. Sho62-202228, Symbol 40 in FIG. 1, for example. The power supply monitoring section monitors conditions of external AC input and DC output from the power supply and reports the results of the monitoring to the host interface control logic section and the interface control logic section of the HDD.

Next, the disk drive will be described. As shown in FIG.13, each disk drive comprises an interface control logic section of the HDD, an HDD and a power supply. The interface control logic section of the HDD transmits/receives data to/from the interface control logic section of the HDD at the disk controller side, and the HDD. The power supply generates predetermined DC output from AC inputs AC2and/or AC3independently prepared for each disk drive, and supplies operating power to the HDD and an interface control logic section of the HDD. See Japanese Patent Application Laid-open Publication No. Sho62-202228, Symbol 20 in FIG. 1, for example.

In the conventional example shown inFIG. 13, an uninterruptible power supply, hereinafter referred to as “UPS” is connected to each of the AC inputs AC1to AC3. If the AC input is normally supplied, each UPS supplies the AC power as received to the power supply of the disk controller or the disk drive. If the AC input fails, each UPS supplies operating power from an auxiliary power supply for backup such as secondary batteries to various sections. For example, when a UPS for the disk controller detects an abnormal condition such as power failure continuing beyond one minute and determines that power is lost, the UPS reports the event to the power monitoring section of the disk controller. The interface control logic section of the HDD which was notified of the power failure by the power monitoring section controls so that the data temporarily stored in the cache memory is written into the HDD of the disk drive, thereby the data is secured when the AC input is lost. This procedure is typically called a destaging.

In the conventional example inFIG. 13, each disk drive is not provided with the power monitoring section. Therefore, a problem will arise when power failure occurs only in the disk drive but not in the disk controller.

One example of the problem is that even if power failure occurred at a certain disk drive, the disk controller is unable to detect the failure since the disk controller is unable to monitor the power condition of the disk drive.

More specifically, when data to be written into the disk drive with power failure is transferred to the disk controller from a host apparatus, the disk controller continues to accept the transferred data to be written since the disk controller is unable to monitor the power condition of the disk drive. The data to be written transferred from the host apparatus is temporarily stored in the cache memory and then transferred to the disk drive which is operating by means of auxiliary power from such as backup batteries. A problem is that the disk controller unable to detect power failure continues to transfer data to the disk drive which is operating on auxiliary power of limited capacity.

Furthermore, considering possibility of continuing data transfer, it is difficult to properly estimate the required capacity for auxiliary power supply. One approach is that time range required for power recovery is estimated first and capacity of auxiliary power supply is determined when maximum time required until the power recovery is assumed. As a result, the dimension for an auxiliary power supply must be maximum for maximum power capacity. On the other hand, if it is of higher priority to make a disk array device as a whole smaller, power capacity must be set minimum for a auxiliary power supply of, minimum dimension. In this case, it is necessary to assume minimum recovery time from power failure. In either case, it is hard to obtain proper capacity for a auxiliary power supply.

SUMMARY OF THE INVENTION

In view of the above problems, one object of the present invention is to provide a method and system for backup power supply for a disk array device which is cost-effective, suitable for downsizing, and improves fault tolerance in power supplying.

One aspect of the present invention is a disk array device having two or more disk units, each disk unit including at least one disk drive, at least either of the disk units having parity bits carrying data recovery information, comprising at least one backup battery provided for each of the disk unit.

Another aspect of the present invention is a power backup system for a disk array device, the disk array device including an error correction group containing a disk unit storing data and a disk unit storing parity bits carrying data recovery information for the disk unit, the disk unit having at least one disk drive, comprising a backup battery provided for each disk unit, a capacity of which determined according to required power for each disk unit.

Yet another aspect of the present invention is a disk array device comprising a disk controller for accepting a request for data transfer from a host apparatus and transmitting and receiving data, a disk drive writing and reading data under control of the disk controller, a power supply monitor provided for each of the disk controller and disk drives, and a backup power supply provided for each disk controller and disk driver, wherein operational power is supplied to the disk controller and the disk drive from the backup power supply according to a monitoring result of the backup power supply, the power supply monitor of each disk drive is connected to the disk controller to have a monitoring result from the power supply monitor of each disk drive received by the disk controller.

Further aspect of the present invention is a method of controlling a disk array device including a disk controller accepting data transfer request from a host apparatus to transmit/receive the data, and a disk drive writing/reading data under control of the disk controller, the respective disk controller and the disk drive having a power supply monitor and a backup power supply, comprising receiving a monitoring result from the power supply monitors of the disk controller and the disk drive respectively, having operational power supplied by the disk controller and the disk drive from the backup power supplies provided thereto respectively according to the monitoring result, and acquiring the monitoring result of the power supply monitor of the disk drive by the disk controller.

Features and objects of the present invention other than the above will become clear by reading the description of the present specification with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

At least the following matters will be made clear by the explanation in the present specification and the description of the accompanying drawings.

FIRST EMBODIMENT OF THE INVENTION

FIG. 1shows a schematic perspective view of a disk array device20andFIG. 2shows a disk subsystem30of the same. First, a configuration of the disk array device20of the present embodiment is described in detail hereinbelow referring to the drawings. The disk array device20comprises a disk controller21and the disk subsystem30. The disk controller21, arranged in the middle of the disk array device20inFIG. 1, is comprised of a cabinet, a fan22for cooling the power supply, a control circuit23including a group of circuit boards for controlling data transfer between a host apparatus, a DC power supply25for supplying DC power to the control circuit23, a breaker box24and the like.

The disk subsystem30includes a cabinet33containing a plurality of disk units32, each comprising a plurality of disk drives31. In each of the disk unit32are installed a plurality of canisters from the front side of the unit32in an attachable and detachable manner constituting a set of disk drive31. Each canister includes an HDA (Hard Disk Assembly) and an electronic circuit for controlling the HDA. In a similar manner, one or two buffer boards34are installed for information transmission between the control circuit23and the canisters as the disk drive31. A fan35is arranged above the canisters and the control circuit23for cooling the equipments.

Further, an AC/DC converter36is installed from the front side of each disk unit32in an attachable and detachable manner for supplying power to the canister31, the buffer boards34, and the fan35. An AC power supply box37supplies AC power to the AC/DC converter36. To each of the AC power supply box37is connected an independent power resource. For example, one AC power supply box may be connected to a commercial power source, and the other AC power supply box37may be connected to a power from a UPS. The power routed through the AC power supply, the AC power supply box37and the AC/DC converter36is normally supplied to the disk unit32and charge the batteries38as a backup power supply.

A capacity of the batteries38is determined according to power demand for each disk unit32. In the present embodiment, the batteries38are provided for each disk unit32. It is to be noted that the disk unit32is sometimes referred to as a hard disk platter, HDD-PL. The hard disk platter is called simply “platter” hereinbelow.

The disk subsystem30of the disk array device20comprises a cabinet containing two sets of error correction groups40at the front and rear part therein, each group40including three disk units32of the above-mentioned structure and a disk unit39for storing parity bits for data recovery information for the disk units32.

In this disk array system, error correction code called parity is generated from the data, and the parities are distributed with the data and stored. Through this distribution of the error correction codes to the respective disks, it becomes realized that the function of an entire system is not lost even if a failure occurs to one disk. Namely, operation with the disk unit39for parity bits enables recovery when the data in other disk unit32has been damaged.

In this respect, if an independent backup battery power supply38is provided for each of the disk units32, normal operation of the disk array device20or reservation of power required for data backup processes is achieved unless all the battery power supplies38are stopped. In other words, technical principle of a disk array system, “improvement in usability” is enhanced to the method of supplying backup power of the present embodiment, and consequently such a disk array device is obtained that is excellent in usability through risk management for failure of all power supplying systems.

FIG. 3Ashows a circuit diagram of a power backup system according to the present embodiment. Three sets of the above-mentioned disk units32as labeled “HDD-PL” in the figure, hereinafter referred to as a “platter” and a set of disk unit39for containing parity bits configure an error correction group40. The disk subsystem30including the error correction group40is controlled by the disk controller21and processes the data in the disk drive31orderly to input/output the data. It is inevitable to supply power for operation of each platter (disk unit)32.

Referring toFIGS. 3B to 3D, the present invention may be applied to disk array devices of various RAID levels.FIG. 3Bshows an example of simple mirroring construction (RAID1) which dispenses with parity bits for error correction.FIG. 3Cshows an exemplary construction in which a disk drive for parity bits are provided for each disk unit. (RAID3/4). In this figure, the disk unit39contains parity bits for error correction. As shown with an alternate long and short dash line, an error correction group40is configured across the plurality of disk units32,39, each of which being provided with AC/DC converters36and a backup battery38. Even if either one of the disk units32,39suffers a power failure, the data in the error correction group40can be recovered by the remaining operative disk units.FIG. 3Dshows an exemplary construction of distributed data guarding (RAID5) in which parity data is stored in each disk drive in each disk unit in distributed manner. In this construction, as described in relation toFIG. 3C, an error correction group40is also arranged across the plurality of disk units. Thus, data protection against a power failure in either disk unit is enhanced for each error correction group40.

It should be noted that the ratio of the number of the disk units for data and the number of the disk units for parity bits in a disk subsystem may be arbitrarily chosen as required. In these cases, a backup power supply may be provided for each disk unit.

In the meantime, the disk unit for data and the disk unit for parity bits are not required to be installed in a single disk subsystem. That is, the disk unit for data and the disk unit for parity bits may be installed in multiple different disk subsystems separately, and a backup power supply may be provided for each disk unit.

In an additional embodiment, multiple disk subsystems are divided into a group for storing data and a group for storing parity bits, a backup power supply may be provided for each subsystem group.

In the present embodiment, AC power is supplied to the AC/DC converter36of each platter32from the AC power supply box37which is provided with AC power from two independent systems such as commercial power source or a UPS. Each AC/DC converter36converts AC power into DC power of suitable current and voltage and supplies the DC power to each platter32to which it is connected. Meanwhile, the DC output from the AC/DC converter36is supplied to the battery38to charge the same.FIG. 4illustrates the schematic power circuit. The AC/DC converter36converts AC 200V from the AC power supply box37into DC48V for example, while attempting improvement of power factor, further stepped down to the voltage required at the platter32, actually the disk drive31and the other devices contained therein, for example 12V and/or 5V. The aforesaid DC48V may be applied to charging if the battery38is not sufficiently charged.

When the AC power supply box37is down or the AC power supply is discontinued due to continuous or instantaneous power failure, or the AC voltage becomes lower than required, such a situation arises that the power of DC48V is unable to be supplied or is not sufficient. In this case, the voltage of the battery38, DC36V becomes relatively higher than the voltage of the power source, and the power flows into the DC-DC converter50of the AC/DC converter36from the battery38. Through this sequence, power backup by the battery38is accomplished in a quick and efficient manner in response to failure in AC power. Moreover, this power backup is performed for each platter32separately to each other, thus is not affected by the power supply systems for the other platters32. In summary, since power backup is provided for each of the platters32and the respective power backup system are independent to each other, this means RAID philosophy for a disk array device has been successfully enhanced to power backup system.

So as to accomplish the aforesaid and other objects, according to another embodiment of the present invention, an AC/DC converter may be provided for each disk unit which is connected to both the AC power source and the battery, to supply power via the AC/DC converter.

Further, the batteries for each disk unit may be stacked.

Moreover, in the aforesaid power backup method for a disk array device, at least a battery is equipped with from among the batteries and the AC/DC converter.

SECOND EMBODIMENT OF THE INVENTION

The second embodiment of the present invention will be described hereinbelow with referring to the accompanying drawings.

As shown inFIG. 5, a disk array device1000(or a storage device, a disk subsystem) comprises a disk controller100and one or a plurality of disk drives200. The disk controller100controls entire operation of the disk array device1000. The disk controller100accepts request for data transfer from a host apparatus or requests a host apparatus to transmit and receive the data. The disk drive200including an HDD (Hard Disk Drive) writes/reads data to/from the HDD under control of the disk controller100. The disk drive200may be equipped additionally as required so as to expand storage capacity of the disk array device1000.

The disk controller100will be described hereinbelow. The disk controller100is comprised of a board containing electronic components for implementing its control functions. Among the electronic components are there a peripheral circuit including a microprocessor, a RAM, a cache memory, a ROM for storing a program for implementing required functions, and dedicated circuits and chips for various functions. As shown inFIG. 5, the disk controller100comprises a host interface control logic section110, a cache memory120, an interface control logic section130of the HDD as well as a power supply140, a power supply monitor150, and a backup battery (auxiliary power source for backup)160.

The host control logic section110implementing interface with a host apparatus carries out processing such as accepting request for data transfer. The cache memory120temporarily stores data to be written to the disk drive200which was transferred from the host apparatus. The interface control logic section130of the HDD carries out interface with the HDD in transmitting/receiving data, i.e., writing data to/reading data from the HDD.

The power supply140generates DC output as required from independent AC input AC1for the disk controller100to supply operational power to the host interface control logic section110, the cache memory120, and the interface control logic section130. To the backup battery160is connected a power supply path to the host interface control logic section110, the cache memory120, and the interface control logic section130. A switch SW is inserted into the power supply path for opening/closing the same which is in turn opened/closed by a selecting signal from the power supply monitor.

The power supply monitor150monitors DC output condition from the power supply40, and notifies the host interface control logic section110and the interface control logic section130of the HDD of the monitoring result. When the power supply monitor150detects abnormality in power supply, the monitor150sends the selecting signal to the switch SW so that operational power is supplied to various sections from the backup battery160.

Next, the disk drive200will be described hereinbelow. As shown inFIG. 5, each disk drive200is provided with a power supply monitor240. Namely, each disk drive200comprises an interface control logic section210of an HDD, a HDD220, a power supply230, the power supply monitor240, and a backup battery (backup auxiliary power supply)250. The interface control logic section210transmits/receives data through the interface control logic section130of the HDD at the disk controller100side. The power supply230generates DC output as required from independent AC input AC2or AC3for each disk drive200to supply operational power to the host interface control logic section210of the HDD and the HDD220. To the backup battery250is connected a power supply path to the host interface control logic section210of the HDD and the HDD220. A switch SW is inserted into the power supply path for opening/closing the same which is in turn opened/closed by a selecting signal from the power supply monitor240.

When an output voltage of the power supply230is determined normal, each power supply monitor240sends a selecting signal to the switch SW so that operational power from the power supply230is distributed to various sections. When the power supply monitor240detects abnormality in output voltage of the power supply230, the monitor240sends the selecting signal to the switch SW so that operational power is supplied to various sections from the backup battery250. When either of the power supply monitors240detects power failure such that power has been lost for over 1 minute for example, the monitor240notifies the host interface control logic section110in the disk controller100and the interface control logic section130of the HDD of the event. The interface control logic section130of the HDD, which was notified by the power supply monitor240at the disk drive200, writes the data temporarily stored in the cache memory120into the HDD220in the disk drive200while each section of the disk drive200is supplied with operational power from the backup battery250. By means of this operation so called “destaging,” reliability of data is ensured even if the AC input AC2and/or AC3is lost.

Typical configuration of the power supply of the disk controller100and the disk drive200may be an AC/DC power supply or a combination of an AC/DC power supply and a DC stabilized power supply (DC-DC converter), which outputs predetermined voltage such as DC12V or 5V. One example of the AC/DC power supply is such a well-known one as described in a distributed publication such as “Transistor Technology Special No. 28, 2nd Edition,” p.7 FIG. 1, CQ Publishing Co. Ltd., Jan. 20, 1993. As the DC stabilized power supply, a well-known regulator may be employed such as a step-down type DC-DC converter, for example, various types of power supply as illustrated in “Transistor Technology Special No. 28, 2nd Edition,” p.4 FIGS. 4–6, CQ Publishing Co. Ltd., Jan. 20, 1993.

The backup battery160,250of the disk controller100and the disk drive200is comprised of a secondary battery such as a lead-acid battery and the like. As shown inFIG. 6, an output voltage of a secondary battery BAT is supplied to the switch SW side through a backflow prevention diode D3. For the backup battery160,250may be employed a variety of alternative devices if only it is an auxiliary power supply which is able to function as an UPS without limited to secondary batteries.

Furthermore, a specific circuit construction of the power supply monitor150,240of the disk controller100and the disk drive200may be configured including predefined logic circuits as shown inFIG. 6, so that an output voltage of the power supply is monitored to determine if it is normal or not to notify the disk controller100of the monitoring result and transmit a selecting signal to the switch SW. The determination section of the monitored voltage may employ a comparator COM. To the input terminals of the comparator COM are inputted a predetermined reference voltage Vref and an output voltage of the power supply at its positive and negative terminals respectively. The output of the comparator COM is inversed when the output voltage of the power supply goes low beyond the reference voltage Vref. The inversed output turns on Transistors Tr1and Tr2. According to the collector signal of the turned on transistor Tr1, the selecting signal is sent to the switch SW to supply operational power to the various sections from the backup battery. Meanwhile, according to the collector signal of the turned on transistor Tr2, abnormality of the power supply is notified to the disk controller100.

An operation for a power failure at the disk drive200will be described more specifically referring to a block diagram inFIG. 7. When the power supply monitor240of the disk drive200detects a fault of the power supply230as indicated by [i] inFIG. 7, operational power is distributed to the various sections from the backup battery250. See [ii] in the figure. At the same time, the power supply monitor240of the disk drive200notifies the host interface control logic section110of the disk controller100and the interface control logic section130of the HDD of the monitoring result as shown by [iii] inFIG. 7. The host interface control logic section110thus notified requests a host apparatus to stop data transfer to the disk drive200to which a power failure occurred. See [iv] in the figure. In response to this operation, the disk controller100stops accepting the request for data transfer to the disk drive200to which a failure occurred. If the data directed to the disk drive of power failure is already written into the cache memory120, the data is read from the cache120and written into the HDD220of the disk drive200of power failure. (Destaging, See [v] in the figure.)

The above configuration enables the disk controller100to receive a notification of power failure from the power supply monitor240of the disk drive200. Thus, in the entire disk array device1000, the disk drive200with power failure is able to be definitely recognized as a part to be excluded from operation. The disk controller100requests a host apparatus to stop data transfer to the disk drive200with power failure and enables to stop the data transfer from the host apparatus. This leads to improvement of reliability in data transfer. Further, even when the power supply for the disk drive200has gone into abnormal state, the backup battery250supplies operational power to the disk drive200. This makes it possible to normally write the data already written into the cache memory120of the disk controller100into the HDD220. Thus, the data up to an instance immediately before occurrence of power failure is able to be protected and reliability in data transfer can be improved. Moreover, the power required to write the maximum amount of data to be cached in the cache memory120into the HDD220of the disk drive200is able to be defined as appropriate capacity of the backup battery250.

Operation of the present embodiment when power failure has occurred to the disk controller will be described referring to a block diagram inFIG. 8. When the power supply monitor150of the disk controller100detects a fault ([i] inFIG. 8), operational power is supplied to the various sections from the backup battery160. See [ii] in the figure. The power supply monitor150of the disk controller100also notifies the host interface control logic section110of the disk controller100and the interface control logic section130of the monitoring result. ([iii] inFIG. 8) The host interface control logic section110notified of power failure by the power supply monitor150requests the host apparatus to stop data transfer. ([iv] inFIG. 8) When the logic section110is notified of power failure from the power supply monitor150, the logic section110requests the host apparatus to stop data transfer. ([iv] inFIG. 8) The logic section110detects the disk driver200that the corresponding power supply monitor240recognizes and notifies normal condition ([v] inFIG. 8), and writes the data already stored in the cache memory120into the HDD220of the normal disk drive200with no power failure. See [vi] inFIG. 8.

Since each disk drive200is provided with the power supply monitor240, the disk drive200in normal operation can be determined. Thus, even if power failure occurs to the disk controller100, the backup battery160supplies operational power to the disk controller100and the data already written in the cache memory120of the disk controller100can be written into the HDD220of the normal disk drive200. Thus, the data up to an instance immediately before occurrence of power failure is able to be protected and reliability in data transfer can be improved.

An example of application of the present invention to virtualization of the disk array device will be described referring to a block diagram ofFIG. 9andFIG. 1as mentioned above. As shown inFIG. 9, the present invention is applied to administration and operation of a plurality of disk drives200as one virtual disk drive, for example. The disk drives200may be located remotely to each other. In the case that power failure has occurred to one of the disk drives200, as shown inFIG. 9andFIG. 1, when the power supply monitor240of the above disk drive200detects a fault of the power supply230([i] inFIG. 9), operational power is supplied to the various sections from the backup battery250([ii] inFIG. 9). The power supply monitor240of the disk drive200also notifies the host interface control logic section110of the disk controller100and the interface control logic section130of the HDD of the monitoring result. ([iii] inFIG. 9) If the data directed to the disk drive200with power failure was already written into the cache memory120of the disk controller100, the logic section 110 of the disk controller100which was notified of the power failure by the monitor240reads the data from the cache memory120and writes it into the HDD220in the other normal disk drive200([v] inFIG. 9). The disk controller100continues operation utilizing the other normal disk drives200until recovery from the power failure ([v] inFIG. 9). The other disk drives200with no power failure including those remotely located notify the disk controller100of their normal operation. ([iv] inFIG. 9) Since the power supply monitor equipped with each disk drive200operates accordingly, the disk array device as a whole is able to maintain normal operation. Thus, even if partial power failure occurs, such processes as writing/reading data can be performed using the disk drives200in normal operation.

Data guarantee using spare disks will be described referring toFIGS. 10A and 10BandFIG. 1mentioned above. In the present embodiment, as shown inFIGS. 10A,10B, the power supply monitors240a,240bof the respective disk drives200aand200bmonitor the condition of power supplying to report it to the disk controller100. The disk controller100performs countermeasures against power failure such as saving the data in response to the report. As shown in the block diagram inFIG. 10B, it becomes possible to write the data to be written into the disk drive200awith power failure originally into the spare disks in a different disk drive200b.

More specifically, as shown inFIGS. 10A and 10BandFIG. 1, when the power supply monitor240of the disk drive200detects failure of the power supply230([i] inFIG. 10B), operational power is distributed to the various sections from the backup battery250([ii] inFIG. 10B). The power supply monitor240of the disk drive200reports the monitoring result to the host interface control logic section110of the disk controller100and the interface control logic section130of the HDD ([iii] inFIG. 10B). If the data directed to the disk drive200with power failure is already stored in the cache memory120of the disk controller100, the logic section110of the disk controller100which was notified of power failure from the monitor240of the disk drive200reads the data from the cache memory120and writes the data into a spare disk in the other disk drive200b([iv] inFIG. 10B). The disk controller100continues its operation using spare disks in a normal disk drive200buntil recovery from the power failure ([v] inFIG. 10B). On the other hand, the disk drives200including those located remotely which do not suffer from the power failure notifies the disk controller100of their normal operation ([iv] inFIG. 10B).

Turning now toFIG. 11, a plurality of disk array devices which are referred to as a “disk subsystem,”1000a,1000bare supplied with power respectively from AC inputs, the distribution switchboards of which being separated to each other, i.e., AC inputs belonging to the different power systems divided by a power source boundary respectively. The data is remotecopied between the disk array devices1000a,1000bwhich are connected to the power sources separate to each other respectively, or is simultaneously written in to the disk array devices1000aand1000bfor “mirroring.” Since the data is remotecopied to the device1000bor is written into the device1000bsimultaneously, the data can be protected even if the disk array device1000agoes down due to power failure.

More specifically, as shown inFIG. 11andFIG. 1, when the power supply monitor150of the disk controller100or the power supply monitor240of the disk drive200detects a failure of the power supply140in the disk array device1000a([i] inFIG. 11), operational power is supplied to the various sections from the backup battery160,250([ii] inFIG. 11). The power supply monitor150of the disk controller100or the power supply monitor240of the disk drive200reports the monitoring result to the host interface control logic section110of the disk controller100or the interface control logic section130of the HDD in the disk array device1000a.When the host interface control logic section110is notified of the power failure from the power supply monitor150in the disk array device1000a,the logic section110requests the host apparatus to stop data transfer and to change the objective device for reading/writing data from the disk array device1000ato the device1000b([iii] inFIG. 11). The disk controller100of the disk array device1000aacknowledges that each of the power supply monitors150,240of the disk array device1000bhave reported normal operation ([iv] inFIG. 11). The disk controller100of the disk array device1000awhich acknowledged normality has necessary data in the disk array device1000acopied to the normal disk array device1000b([v] inFIG. 11). Accordingly, the host apparatus changes the objective device for reading/writing data from the original disk array device1000ato the device1000b([vi] inFIG. 11).

According to the preferred embodiments of the present invention, the following effects can be accomplished.

Since the disk controller is capable of receiving a report regarding failure from the power supply monitor of the disk drive, the disk drive having power failure can be identified to be a section in which operation should be stopped in the entire disk array device. Thus, the disk controller is capable of requesting the host apparatus to stop data transfer to the disk drive with power failure to stop the data transfer. Accordingly, improvement of reliability in data transfer is accomplished.

Since the data already stored in the cache memory of the disk controller is able to be normally written into the HDD of the disk drive to which power failure has not occurred, reliability in data transfer can be improved.

Further, a proper capacity of the backup power supply may be defined as the power required for writing the maximum data storable in the cache memory into the HDD of the disk drive.

Providing the power supply monitor to each of the disk drives enables identification of the disk drives capable of normal operation. Thus, even if power failure has occurred to the disk controller, it is possible to write the data already stored in the cache memory into the HDD of the normal disk drive and reliability in data transfer is improved.

It is possible to provide a method of power backup for disk array devices which is cost-effective and suitable for downsizing, and also achieves fault tolerance in power supplying, thus reliability of disk array devices is improved.