Disc access control method for cache-embedded disc control apparatus with function-degradation capability of data transmission path

We claim:

1. In a disk control apparatus for controlling access from a plurality of channels for supplying access requests, to a plurality of disks for reading and writing data, wherein the disk control apparatus includes a cache for storing a copy of the data stored on said disks, a plurality of storage paths each being responsive to access requests received from said channels for reading and writing data stored in said cache and on said disks and a control memory for storing access control information used by said storage paths to control access by said storage paths to said cache and to said disks in response to an access request received from one of said channels, a disk access control method comprising the steps of:

(a) accessing said control memory to obtain access control information indicating functional level of a storage path which receives an access request from a channel for accessing a designated disk and to obtain access control information indicating a functional level of said designated disk;

(b) determining whether said storage path which receives said access request is capable of executing the requested access and whether this type of access is permitted by comparing said functional level of said storage path with said functional level of said designated disk; and

(c) controlling said storage path to access said cache and/or said designated disk to read and/or write data in accordance with the ability of the storage path to execute the requested access and the functional level of said designated disk;

wherein the functional levels of said storage path include:

(i) a functional level at which a disk can be read/written directly via a storage path and at which the cache can be read/written via a storage path,

(ii) a functional level at which a disk can be read/written directly .via a storage path and at which the cache can be only read via a storage path,

(iii) a functional level at which a disk can be directly read/written via a storage path and at which the cache cannot be accessed via a storage path, and

(iv) a functional level at which a data access to a disk cannot be performed by a storage path because of a disk failure,

wherein said functional level (i) is the highest level followed by said functional levels (ii) , (iii) and (iv).

2. A disk access control method according to claim 33, wherein said step (b) comprises:

(b1) determining from said access control information a functional level of said storage path indicative of a type of cache use available to said storage path, said type of cache use is one of three types including (i) a first type representing that the cache is usable for read/write, (ii) a second type representing that the cache is usable only for read, and (iii) a third type representing that the cache is not usable, the functional level of the first type being the highest followed by the second type (ii) and the third type (iii);

(b2) determining from said access control information an access level for said designated disk indicative of the lowest functional level required for a storage path to access said designated disk; and

(b3) determining that said storage path, which receives said access request, is capable of executing said access request when the functional level of said storage path is at least equal to the access level of said designated disk.

3. A disk access control method according to claim 2, wherein said step (b) further includes:

(b4) lowering the access level of said designated disk when no storage path has a functional level which is at least equal to the access level of said designated disk as stored in said control memory.

4. A disk access control method according to claim 3, wherein the access levels of said disks include:

(1) an access level at which a disk can be accessed only from the storage paths having the functional level (i);

(2) an access level at which a disk can be accessed only from the storage paths having the functional levels (i) or (ii);

(3) an access level at which a disk can be accessed from the storage paths having the functional levels (i), (ii) or (iii); and

(4) access level at which disk access is inhibited regardless of the functional level of the storage path.

5. A disk access control method according to claim 4, further comprising the steps of:

(d) setting the access level of all disks to level (1) when the cache is disconnected; and

(e) setting the access level of all disks to level (3) when the cache is reconnected.

6. A disk access control method according to claim 3, further comprising the step of:

(d) setting the functional level of a storage path which has recovered from a fault to one of the functional levels (i), (ii) and (iii) in accordance with the access level of the storage path after repair of the storage path.

7. A disk access control method according to claim 3, further comprising the steps of:

(d) interrupting a connection between a disk and at least one storage path for performing an operation of closing at least one storage path for maintenance of the at least one storage path by temporarily setting the functional level of the storage path to level (iv); and

(e) after the maintenance of the at least one storage path operation, opening the at least one storage path by setting the functional level of the at least one storage path to one of the functional levels (i), (ii), and (iii).

8. A disk access control method according to claim 3, wherein said disk control apparatus further includes a back-up memory, and wherein said method further comprises the steps of:

(d) storing data in said back-up memory at the time said data is written in said cache in response to an access request designating a particular disk; and

(e) transferring data stored in said back-up memory from the back-up memory to the disk asynchronously withstoring data in said back-up memory.

9. A disk access control method according to claim 8, further including the steps of:

(f) setting the access level of all disks to level (1) when said back-up memory is disconnected; and

(g) setting the access level of all disks to level (3) when said back-up memory is reconnected.

10. A disk access control method according to claim 1, further including the steps of:

(d) detecting an error during a data access involving a particular storage path; and

(e) regenerating a current functional level of the particular storage path as indicated by the access control information stored in said control memory to designate a new functional level which is more restrictive concerning accesses to said cache than said previous functional level.

11. A disk access control method according to claim 10, wherein said step (e) comprises:

(e1) setting a new functional level for said particular storage path based on the new cache functional level which has been reduced to the occurrence of each path fault.

12. A disk access control method according to claim 10, wherein said step (e) comprises:

(e2) closing said particular storage path; and

(e3) selecting another storage path for accessing said designated disk by evaluating the functional levels of storage paths, other than said particular storage path, which are accessible to said designated disk and are unclosed.

13. A disk access control method according to claim 1, further including the steps of:

(d) determining from said access information in said control memory the functional level for all storage paths from which said designated disk is accessible;

(e) selecting the highest functional level of the functional levels determined in step (d) for storage paths having a functional level higher than the access level of the designated disk; and

(f) setting the access level of the access control information for the designated disk as stored in said control memory to be equal to the functional level selected in step (e).

14. A disk access control method according to claim 1, further including the steps:

(d) storing, as part of said access control information in said control memory, a request flag indicating a change of an access level of a disk when the functional level of a storage path connected to the disk has been changed due to occurrences of faults in a storage path and/or cache due to maintenance for recovery of the storage path and/or cache; and

(e) changing the access level of said disk based on the functional level of information of storage paths connected to said disk.

15. A disk access control method according to claim 1, wherein said disk control apparatus further includes a back-up memory and wherein said method further comprises the steps of:

(d) storing data in said back-up memory at the time said data is written in said cache in response to an access request designating a particular disk; and

(e) transferring data stored in said back-up memory from the back-up memory to the disk asynchronously with storing data in back-up memory.

16. A disk access control method according to claim 15, wherein the functional levels of said storage paths includes:

(i) a level at which direct access is possible via a storage path between a channel and a disk, at which access is possible via a storage path between a channel and the cache, and at which access is possible via a storage path between a channel and said backup memory;

(ii) a level at which direct access is possible via a storage path between a channel and a disk, at which access is possible via a storage path between a channel and the cache and at which access is possible via a storage path between a disk and the cache;

(iii) a level at which direct access is possible via a storage path between a channel and a disk and at which access is possible via a storage path between a channel and the cache;

(iv) a level at which direct access is possible via a storage path between a channel and a disk and at which access is possible via a storage path between a disk and the cache; and

(v) a level at which direct access is possible via a storage path between a channel and a disk.

17. A disk access control method according to claim 16, further including the steps of:

(f) regenerating to one of the functional levels (i), (ii) , (iii) , (iv) and (v) the functional level of a storage path which experiences a fault therein or closing the storage path in accordance with the degree of the fault, wherein the degree of fault is classified into three types including

degree-1 wherein the cache is accessible and the back-up memory is not accessible,

degree-2 wherein the cache is not accessible, and

degree-3 wherein the disk is not accessible; and

selecting a storage path based on a value of functional levels of unclosed storage paths connected to the disks controlled by the disk control apparatus.

18. A disk access control method according to claim 16, further including the steps of:

(f) setting the functional level of a storage path which has recovered from a fault to one of the functional levels (v), (iv), (iii), (ii) and (i) in accordance with the degree of recovery of the storage path, wherein the degree of recovery is classified into three types including

degree-1 wherein the disk is accessible, the cache is not accessible and the back-up memory is not accessible,

degree-2 wherein the disk is accessible, the cache is accessible and the back-up memory is accessible,

degree-3 wherein the disk is accessible, the cache is accessible and the back-up memory is accessible; and

(g) executing access in accordance with a combination of functional levels of at least one storage path connected to the disks controlled by the disk control apparatus.

19. A disk access control method according to claim 15, further including the steps of: (f) determining if there is any storage path capable of executing access to a disk at an access level if there is any storage path capable of receiving an initial start-up signal from a channel and one storage path capable of receiving a report on the completion of a SEEKing operation from a disk at the access level and determining, whether those storage paths are the same or not;

(g) counting the number of storage paths capable of executing access at each access level; and

(h) seeking as the access level of the disk the highest functional level of the storage paths, the total number of storage paths which exceeds a threshold value.

20. A disk access control method according to claim 1, further comprising the steps of:

(d) increasing the number of storage paths by constituting each storage path with two or more processors, and connecting the processors using cross paths between said processors.

21. In a disk control apparatus for controlling access from a plurality of channels for supplying access requests, to a plurality of disks for reading and writing data, wherein the disk control apparatus includes a cache for storing a copy of the data stored on said disks, a plurality of storage paths each being responsive to access requests received from said channels for reading and writing data stored in said cache and on said disks and a control memory for storing access control information used by said storage paths to control access by said storage paths to said cache and to said disks in response to an access request received from one of said channels, a disk access control method comprising the steps of:

(a) storing in said control memory a highest ranking value of functional levels of data transfer paths of each storage path, said highest ranking value being stored in correspondence to said each storage path, wherein each of said plurality of storage paths includes therein a plurality of arbitrarily selectable and usable data transfer paths so that said each storage path performs data transfer between a channel and a disk, and/or said cache, and a ranking value of each data transfer path in each storage path is defined as a functional level of said each data transfer path, said ranking value being assigned to each data transfer path in correspondence to an inclusion relation of data transfer function executed by said each storage path, and storing in said control memory an access level for respective disk, said access level being stored in correspondence to each disk, said access level representing a functional level so that all said storage paths accessing a designated disk or said cache storing data of said designated disk are restricted to use a data transfer path in each storage path having a same functional level indicated by an access level of said designated disk in order to transfer the data of said designated disk or the data of said designated disk stored in said cache;

(b) comparing, in response to a storage path which receives an access request from a channel for accessing a designated disk or said cache storing data of said designated disk, the ranking value of said storage path stored in said control memory with a value of the access level of said designated disk stored in said control memory, and judging whether said functional level is equal to or higher than said access level, to thereby determine that said storage path is capable of executing the requested access to said designated disk; and

(c) selecting, in response to said storage path which is determined to be capable of executing the requested access to said designated disk, selecting a data transfer path corresponding to a functional level which is the same as the access level of said designated disk, and transferring the data of said designated disk or data of said cache storing the data of said designated disk by using said selected data transfer path wherein the functional levels of said storage path include:

(i) a functional level at which a disk can be read/written directly vial a storage path and at which the cache can be read/written via a storage path,

(ii) a functional level at which a disk can be read/written directly via a storage path and at which the cache can be only read via a storage path,

(iii) a functional level at which a disk can be directly read/written via a storage path and at which the cache cannot be accessed via a storage path, and

(iv) a functional level at which a data access to a disk cannot be performed by a storage path because of a disk failure,

wherein said functional level (i) is the highest level followed by said functional levels (ii), (iii) and (iv).

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention relates to a disc access control method and apparatus, and more particularly to a method and an apparatus, including a cache memory, which are suitable for control of the degeneration of a disc access function due to errors and for recovery of the disc access function.

In a conventional disc control apparatus, having a cache, frequently accessed data is stored in the cache and is read from the cache, without access to a disc, to improve the efficiency of accessing data. As described in Japanese Patent Publication JP-A-60-79447, if a problem in the cache is detected for any one of the storage paths, the whole cache is disconnected and all reading/writing of data in the cache via other storage paths is discontinued. By disconnecting the whole cache, the storage path, which can no longer correctly read/write in the cache, directly updates records on the disc, while other access paths, which can correctly read/write in the cache, are prevented from reading old data from the records in the cache, thereby preventing transfer of old data, which is different from the latest data stored on the disc (hereinafter referred to as a data change condition).

In the conventional disc control apparatus, if any one of the storage paths detects a problem within the cache, the error is regarded as an error in the whole cache, and the cache is disconnected from the disc control apparatus. However, an error on the side of the storage path may appear as a cache error, in which case the cache is disconnected, although there may be many remaining storage paths which can be used to read/write in the cache correctly. Therefore, the usability of the cache is greatly reduced.

A method is conceivable in which a storage path in which a cache error has been detected is closed and the use of the cache by another storage path which can be used to correctly read/write in the cache is continued to be used, thereby increasing the usability of the cache and preventing a data change condition from occurring. However, according to this method, the direct access to a disc by a storage path, in which a cache error has been detected, is also discontinued. Therefore, if there is a disc connected to only the access path in which the cache error has been detected, it will not be possible to access that disc at all.

On the other hand, if a disc is accessed directly, a different data transfer path is used, depending on whether data to be accessed is present in the cache, so that even those storage paths, which have experienced an error in accessing the cache, can access the disc. Therefore, there is the problem that the storage paths are not utilized effectively.

SUMMARY OF THE INVENTION

It is an object of the present invention to increase the usability of a disc control apparatus and to prevent the occurrence of a data change condition.

It is another object of the present invention to facilitate the maintenance which is performed during the operation of a disc control apparatus.

A disc control apparatus according to the present invention, includes a plurality of channels, discs for storing data, a plurality of storage paths provide which for parallel processing of data being transferred between the channels and the discs, a cache for storing a copy of part of the data stored on the disc, and a control memory for controlling access to the plurality of storage paths. The disc control apparatus stored a reference for selecting an executable storage path in the control memory in order to achieve the above objects.

A method of controlling the disc control apparatus according to the present invention will now be described more specifically. A functional level indicative of a type of cache use by a storage path which connects a channel and a disc is provided as a reference in that storage path. Also, an access level which defines a functional level which a storage path capable of accessing a disc should have, at the least, is provided in that disc, which is controlled by the disc control apparatus. Only a storage path having a functional level higher than the access level of a disc to be accessed will be permitted to access that disc. A criterion for selecting a storage path used when an initial start-up command is received from a channel, and a criterion for selecting a storage path used for connection to a disc, when a report on the completion of the SEEKing operation (involving the positioning of a magnetic head) from the disc is received, are changed to select an available storage path having the necessary functional level each time an initial start-up command and report is received.

As mentioned above, the disc to be accessed is accessed in conformity with a functional level designated as an access level in the disc, using only a storage path having a functional level higher than the one designated as the access level in the disc. This prevents the plurality of storage paths from accessing the disc at different functional levels, to thereby prevent a data change condition which would otherwise occur. By setting the access level set in the disc at the highest possible level, in a range of conditions where storage paths which can access the disc can exist, an optimal type of cache use, when a storage path accesses the disc, is selected optimally in that disc, and the problem of reduction in the usability of the cache is solved.

When an error occurs, the functions of the storage paths vary from storage path to storage path. In such a case, a criterion for selecting a storage path to be used when an initial start-up command is received from a channel, and a criterion for selecting a storage path to be used when a report on the completion of the SEEKing operation is received from the disc, are changed to enable the use of a storage path which can be used in only one of the two cases, where the initial start-up command is received and when the report is received, in the other of the two cases to thereby increase the number of storage paths available. The presence of one storage path, which can receive an initial start-up from a channel, and another storage path, which can receive a report on the completion of the SEEKing operation from a disc, serves to determine that there is one normal storage path to thereby increase the usability of the storage paths. Thus, the degree of cache use can be selected optimally for each disc to prevent reduction in the usability of the cache.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a disc subsystem and a disc control apparatus representing an embodiment of the present invention.

FIG. 2 illustrates the contents of a common control memory are used in the disc control apparatus.

FIG. 3 is a flowchart showing the operation procedures of the respective storage paths in the disc control apparatus.

FIG. 4 is a flowchart explaining the details of a procedure for determining the permission/rejection of access in the operation of each storage path in FIG. 1.

FIG. 5 is a flowchart explaining the details of a procedure (1) for changing the access level in a disc in the operation of a storage path.

FIG. 6 is a flowchart explaining the details of a procedure (2) for changing the access level of a disc in the operation of a storage path.

FIG. 7 is a flowchart explaining the details of a procedure for setting a factor of storage path error in the operation of a storage path.

FIG. 8 is a flowchart for explaining storage path functional levels in the operation of a storage path.

FIG. 9 illustrates an embodiment of one logical storage path, including two modules.

FIG. 10 illustrates the structure of a table which manages the status of two modules constituting a logical storage path.

FIG. 11 illustrates a decision table which gives the relationship between the status of a logical storage path and the status of two modules constituting the storage path.

FIG. 12 illustrates the structure of a logical storage path in which two modules constituting a logical storage path and two modules consisting of another logical storage path have a cross path.

FIG. 13 is a flowchart showing the procedures executed by a disc control apparatus with a cache to which the present invention is applied.

FIG. 14 is a block diagram of a disc subsystem, including a disc control apparatus with a cache, according to the present invention.

FIG. 15 illustrates data, in a table format, necessary for control using the present invention.

FIG. 16 is a list of routes used for transfer of data.

FIG. 17 is a flowchart showing a procedure for determining an access level.

FIG. 18 illustrates the relationship between SP-LEVEL and SP-STATUS used for changing the functional level of the storage path.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment directed to setting a functional level of a storage path as a reference level will now be described.

FIG. 1 is a block diagram of a disc subsystem, to which the present invention is applied. The disc subsystem includes a channel control unit 111, a disc control apparatus 110, discs 90-93, connection lines 113-120 which connect the channel control unit 111 and the disc control apparatus 110, and connection lines 137-152 which connect the disc control apparatus and the discs 90-93. The discs 90-93 may be magnetic discs, optical discs or semiconductor discs.

The channel control unit 111 includes eight channels a-h through which requests for access to the discs 90-93 can be made simultaneously. The disc control apparatus 110 includes data transfer control units 100-103 (referred to hereinafter as storage paths (SP)), which receive requests for access to data from the channels and transfer (read/write) data between the channels and the discs in a parallel manner. Specifically, each storage path is realized by a special-purpose processor or a general-purpose microprocessor. The connections between the eight channels a-h and the four storage paths 100-103 are controlled in a dynamic switching manner by a Multi-Path switching Device 100, such that requests for access from the channels via the connection lines 121-124 are not collectively received by any particular storage path SP. The disc control apparatus 110 further includes a cache 105, which is connected to storage paths (1)-(4) via connection lines 126, 128, 130 and 132, respectively, and a back-up memory (NVS) 106, which is connected to storage paths (1)-(4) via connection lines 133-136, respectively. The disk control apparatus 110 includes the connection lines 137-140 which connect the storage paths 100-103 to the disks 90-93. As described in the foregoing, each storage path includes data transfer paths respectively connecting the storage path itself to the channels, cache, backup memory and disks. Accordingly, the storage path can be considered to be an aggregation of three kinds of data transfer paths including a data transfer path for performing read/write between the channels and the cache, a data transfer path for performing read/write between the channels and the backup memory, and a data transfer path for performing read/write between the channels and the disks. In other words, the storage path has a function to arbitrarily select one of these data transfer paths included in the storage path itself, and to perform desired data transfer. The cache 105 is a volatile memory which stores a copy of a part of the data stored in discs 90-93.

When a storage path SP receives from a channel a request for access (read) to data previously stored in the cache 105 (such a request for access is referred to hereinafter as a cache hitting access request), it reads the data in the cache 105, instead of reading the data from the discs 90-93, to increase the responsiveness of access to the data. If the cache hitting access request is a write request, the storage path SP updates the data previously stored in the cache 105 and simultaneously writes the same updating data into the back-up memory (NVS) 106, which is a volatile memory for backing up the updating data in the cache, to terminate the processing for the write request from the channel only by updating the data in the cache, without updating the data stored on the discs 90-93. Later, the storage path SP writes the new data updated only in the cache onto the disc, during an available time after data transmission between the disc control apparatus 110 and the channel, using the data stored in the back-up memory 106, to thereby increase the responsiveness of access to the write request (referred to as a disc high-speed write).

A control memory 104, which is connected to storage paths (1)-(4) via connection lines 125, 129, 131 and 127, respectively, is a memory to be referred to when the four storage paths (1)-(4) in the disc control apparatus 110 process an access request. This control memory 104 stores data as shown in FIG. 2 in the form of a table.

Referring to FIG. 2, a SP-LEVEL table 200 stores one of the following three functional levels, which are set according to current cache status, as a functional level indicative of the type of cache use available to the respective storage paths depending on the respective degrees of error experienced in the storage paths (1)-(4):

(1) Functional level 3 at which a channel can directly read a disc and write data onto the disc via a storage path, and can read the cache and write data into the cache via the storage path between the channel and the cache;

(2) Functional level 2 at which a channel can directly read a disc and write data onto the disc via a storage path, and can only read the cache via the storage path between the channel and the cache; and

(3) Functional level 1 at which a channel can directly read a disc and write data onto the disc via a storage path, and can neither read the cache, nor write data into the cache, via the storage path between the channel and the cache.

In the example illustrated in FIG. 2, the level 3 is set as the initial functional level of all the storage paths in the SP-LEVEL table 200. A flag indicative of whether each of the four storage paths (1)-(4) in the disc control apparatus 110 is logically available or not ("1" indicates that a storage path SP is available, and "0" indicates that a storage path SP is not available) is also set in a SP-AVAILABLE table 210. In the example illustrated in FIG. 2, the flags for all the storage paths are set in table 210 so as to indicate that all storage paths are logically available. A flag indicative of whether each of the storage paths (1)-(4) is functionally available ("1" indicates that a storage path SP is available and "0" indicates that a storage path SP is not available) is set in a SP-OPERABLE table 220. In FIG. 2, the flags for all of the storage paths are shown as being set to indicate that all storage paths are functionally available. The functional levels of the storage paths as set in the SP LEVEL table 200 make sense only when the storage paths are functionally available.

A path functional level (access level) that a storage path must have to access a disc, as a minimum, is set as a variable in a (LEVEL) column for each of the DEV rows (1)-(4) of a DEV table 230, each row of which correspond to a respective disc. The following four access levels are provided:

(a) Access level 3 which allows the disc to be accessible from only a storage path at the functional level 3;

(b) Access level 2 which allows the disc to be accessible from only a storage path at the functional level 2 or 3;

(c) Access level 1 which allows the disc to be accessible from a storage path at the functional level 1, 2 or 3; and

(d) Access level 0 which inhibits any access to the disc.

In the example of FIG. 2, the variables in the column (LEVEL) for rows DEV (1)-(4) indicative of access levels of the discs 90-93 are all set to level 3. The contents of columns (FLAG) and (LOCK) in DEV table 230 will be described later.

The structure of an access path between a disc and a channel controlled by the disc control apparatus 110 is set in a DCB table 240 in correspondence to that disc. More specifically, the structure of an access path present between a disc and a channel is set as three data values PAM, POM and CPAS for each of the discs 90-93 in DCBs (1)-(4). A flag indicative of which of the storage paths (1)-(4) in the disc control apparatus each disc is logically connected to ("1" indicates the presence of connection and "0" indicates the absence of connection) is set in columns (b1)-(b4) of the row PAM. In the example of FIG. 2, since discs 90 and 91 are connected to all storage paths (1)-(4) via paths 137-140, the columns (b1)-(b4) of the row PAM of DCBs (1) and (2) are all set to "1". Since discs 92 and 93 are connected to only storage paths (2) and (3) via paths 138 and 139, values of PAM for the (b1) and (b4) columns of DCBs (3) and (4) are set to "1" and the remaining ones are set to "0". A flag indicative of which of the storage paths (1)-(4) in the disc control apparatus can functionally access any particular disc ("1" indicates that a storage path SP can access the disc and "0" indicates that a storage path SP cannot access the disc) is set in each of (b1)-(b4) columns of the row POM. In FIG. 2, the POM values in the columns (b1)-(b4) for the DCBs (1)-(4) are all set to "1". The results of ANDing the corresponding bits for PAM and POM in the respective (b1)-(b4) columns of the DCB table 240 are set in the row CPAS of the DCBs (1)-(4). Specifically, CPAS values of the respective columns (b1)-(b4) show, in correspondence to a disc, a flag indicative of one of