Method of allocating raid group members in a mass storage system
There are provides an allocation module and a method of allocating a logical disk to a next member of a given RAID group. The method comprises: identifying one or more physical disks comprising at least one logical disk with already allocated member of said given RAID group, thus giving rise to allocated physical disks; identifying one or more pairs constituted by at least one allocated physical disk with non-allocated physical disks, said pairs having minimal number of RAID groups with members allocated to both physical disks in the pair, thus giving rise to a first group of pairs with minimal contention value; and selecting among the first group of pairs with minimal contention value one or more non-allocated physical disks as candidate physical disks for allocating said next member MEM i+1 of said given RAID group, wherein 0<i<N+1. The method further comprises identifying among one or more disk units corresponding to one or more selected candidate physical disks at least one disk unit matching a reliability criterion; identifying at least one candidate physical disk corresponding to the at least one identified disk unit; and allocating said next member of said given RAID group to a free logical disk in the identified at least one candidate physical disk.
1. For use with a storage system comprising a plurality of physical disks constituting a physical storage space, and a plurality of disk units, each comprising several of the plurality of physical disks, said physical storage space is configured as a concatenation of a plurality of RAID (Redundant Array of Independent Disks) groups, each RAID group comprising N+2 members; wherein the RAID groups are configured as RAID 6 groups and the number of members of a RAID group equals twice the number of disk units; a method of allocating a physical disk to a group member of a given RAID group, the method comprising:
characterizing each pair of physical disks of the plurality of physical disks by a contention value being a number of RAID groups with members allocated to both physical disks in the pair;
identifying among multiple pairs of physical disks one or more pairs having a minimal contention value, the minimal contention value being a contention value that is a minimum of contention values of all pairs;
allocating said group member to a certain physical disk selected from physical disks comprised in said one or more pairs; wherein the allocating is performed such that every disk unit comprises no more than two allocated group members of said given RAID group.
2. The method of claim 1 further comprising identifying a disk unit matching a reliability criterion; wherein the certain physical disk that is used for allocating the group member is comprised in the disk unit.
3. The method of claim l wherein there are identified more than one disk units matching the reliability criterion, the method further comprising selecting, among the identified disk units, the disk unit for allocation of the group member of said given RAID group.
4. The method of claim 2 comprising identifying one or more candidate physical disks from the physical disks comprised in said one or more pairs, selecting, among the one or more candidate physical disks, the certain physical disk for allocation of the group member of said given RAID group, wherein the selection is provided in accordance with at least one criterion characterizing the physical disks and selected from the group comprising: occupancy of the physical disks; the lowest sequence number; the highest performance characteristics; performance characteristics within a certain range; the highest reliability characteristics; reliability characteristics matching a certain range.
5. The method of claim 2 wherein at least one of the operations:
identifying one or more pairs and identifying a disk unit matching the reliability criterion, is provided until a predefined number of matches are made.
6. The method of claim 1 further comprising selecting among the one or more pairs with minimal contention value all non-allocated physical disks as candidates for allocation to said group member.
7. The method of claim 1 wherein the percentage of common data shared between two physical disks is characterized by a number of members in a RAID group divided by a number of physical disks in the storage system.
8. The method of claim 1 operative for at least one process selected from the group comprising:
allocating one or more new RAID groups;
re-allocating existing RAID groups in case of a disk and/or disk unit failure; and
re-allocating existing RAID groups in case of a new disk and/or disk unit.
9. The method of claim 1 wherein the storage system is configured in accordance with the RAID 6 protection scheme, and wherein rebuilding after two concurrent failures is first provided to the members of RAID groups that are common to respective failed disks.
10. A computer program comprising computer program code means for performing all the steps of claim 1 when said program is run on a computer.
11. A computer program as claimed in claim 10 embodied on a computer readable medium.
12. For use with a storage system comprising a plurality of physical disks constituting a physical storage space, and a plurality of disk units, each comprising several of the plurality of physical disks, said physical storage space is configured as a concatenation of a plurality of RAID (Redundant Array of Independent Disks) groups, each RAID group comprising N+2 members; a method of allocating a physical disk to a group member of a given RAID group, the method comprising:
characterizing each pair of physical disks of the plurality of physical disks by a contention value being a number of RAID groups with members allocated to both physical disks in the pair;
identifying among multiple pairs of physical disks one or more pairs having a minimal contention value, the minimal contention value being a contention value that is a minimum of contention values of all pairs;
identifying one or more candidate physical disks among the physical disks comprised in said one or more pairs,;
identifying among disk units comprising the one or more candidate physical disks at least one disk unit matching a reliability criterion; and identifying at least one candidate physical disk corresponding to the at least one disk unit;
selecting, from the at least one candidate physical disk, a certain physical disk for allocation of the group member of said given RAID group, wherein the selection is provided in accordance with at least one criterion characterizing the physical disks and selected from the group consisting of: occupancy of the physical disks; the lowest sequence number; the highest performance characteristics; performance characteristics within a certain range; the highest reliability characteristics; and reliability characteristics matching a certain range:, and
allocating said group member of said given RAID group to the certain physical disk.
13. A storage system comprising a plurality of physical disks constituting a physical storage space, and an allocation module operatively connected to a plurality of disk units, each disk unit comprising several of the plurality of physical disks, each physical disk configured to comprise a plurality of logical disks, said physical storage space is configured as a concatenation of a plurality of RAID 6 (Redundant Array of Independent Disks) groups, each RAID group comprising N+2 members; wherein the number of members of a RAID group equals twice the number of disk units in the storage system, wherein every disk unit comprises logical disks allocated to members of each RAID group, and wherein there are two logical disks in each disk unit allocated to a certain RAID group, the allocation module further operable:
to characterize each pair of physical disks of the plurality of physical disks by a contention value being a number of RAID groups with members allocated to both physical disks in the pair;
to identify one or more pairs having a minimal contention value, the minimal contention value being a contention value that is a minimum of contention values of all pairs; and
to allocate said group member of said given RAID group to a certain physical disk among physical disks comprised in said one or more pairs.
14. The storage system of claim 13 further comprising a plurality of disk units, each comprising several of the plurality of physical disks, wherein the allocation module is operable to identify a disk unit matching a reliability criterion; wherein the certain physical disk selected for allocating the group member is comprised in the disk unit.
15. The storage system of claim 14 wherein the RAID groups are configured as RAID 6 groups, and wherein the allocation module is configured to allocate said group member to said certain physical disk in accordance with a reliability criterion that requires that a matching disk unit comprises no more than two members of said given RAID group.
16. The storage system of claim 14 further operable to provide at least one of the operations: identifying one or more pairs, and identifying disk units matching the reliability criterion until a predefined number of matches are made.
17. A storage system comprising a plurality of physical disks constituting a physical storage space, a plurality of disk units, each comprising several of the plurality of physical disks, and an allocation module, said physical storage space is configured as a concatenation of a plurality of RAID (Redundant Array of Independent Disks) groups, each RAID group comprising N+2 members; the allocation module further operable:
to characterize each pair of physical disks of the plurality of physical disks by a contention value being a number of RAID groups with members allocated to both physical disks in the pair;
to identify one or more s airs having a minimal contention value the minimal contention value being a contention value that is a minimum of contention values of all pairs;
to identify among the disk units at least one disk unit matching a reliability criterion; to identify a certain physical disk among the physical disks comprised in said one or more pairs and further comprised in the at least one disk unit; and
to allocate said group member of said given RAID group to the certain physical disk.
18. The storage system of claim 13 wherein the percentage of common data shared between two physical disks is characterized by a number of members in a RAID group divided by a number of physical disks in the storage system.
19. The storage system of claim 18 operable, in case of rebuilding after two concurrent failures, first to rebuild the members of RAID groups that are common to respective failed disks.