Declustered array capacity

The mmvdisk command keeps track of the total raw capacity in each user declustered array. The capacity is raw in that it does not account for RAID code redundancy and vdisk metadata overhead. This is the capacity available for defining vdisk sets.

The total raw capacity of a declustered array depends on several factors. The most important factors are the number and size of the pdisks, and the number of equivalent pdisk spares in the declustered array. The size of the pdisks in turn affects the pdisk partition size and number of partitions per pdisk, which also affects the total raw capacity. A portion of each pdisk is reserved for log group atomic updates and for other metadata.

The presence of log home vdisks in a user declustered array also subtracts from the total raw capacity.

The mmvdisk command displays the total and free raw capacity of user declustered arrays in several output listings. The most useful is the declustered array section of the mmvdisk vdiskset list command, which is used for sizing vdisk sets into declustered arrays:


# mmvdisk vdiskset list --recovery-group RG01

                declustered                 capacity            all vdisk sets defined
recovery group     array     type  total raw  free raw  free%  in the declustered array
--------------  -----------  ----  ---------  --------  -----  ------------------------
RG01            DA1          SSD    2288 GiB  1144 GiB    50%  DA1.VS1
RG01            DA2          HDD    3330 GiB   833 GiB    25%  DA2.VS1

mmvdisk: Total capacity is the raw space before any vdisk set definitions.
mmvdisk: Free capacity is what remains for additional vdisk set definitions.

The mmvdisk recoverygroup list --declustered-array command gives a different view that omits the vdisk sets, but includes the number of vdisks, pdisks, and spares:


# mmvdisk recoverygroup list --recovery-group RG01 --declustered-array

declustered   needs          vdisks      pdisks     replace        capacity
   array     service  type  user log  total spare  threshold  total raw free raw  background task
-----------  -------  ----  ---- ---  ----- -----  ---------  --------- --------  ---------------
DA1          no       SSD      8   9      8     2          2   2288 GiB 1144 GiB  scrub 14d (87%)
DA2          no       HDD      8   0     20     3          2   3330 GiB  833 GiB  scrub 14d (86%)

mmvdisk: Total capacity is the raw space before any vdisk set definitions.
mmvdisk: Free capacity is what remains for additional vdisk set definitions.