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

Claim 2

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).

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 8

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).

Claim 9

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.

Claim 10

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.

Claim 11

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.

Claim 12

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.

Claim 13

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.

Claim 14

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).

Claim 15

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.

Claim 16

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.

Claim 17

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.

Claim 18

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.

Claim 19

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.

Claim 20

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.

Claim 21

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.

Claim 22

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).

Claim 23

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).