What happens when you add larger disks to an aggregate

What Data ONTAP does when you add disks to an aggregate that are larger than the existing disks depends on the RAID level (RAID4 or RAID-DP) of the aggregate.

When an aggregate configured for RAID4 protection is created, Data ONTAP assigns the role of parity disk to the largest disk in each RAID group.
When an existing RAID4 group is assigned an additional disk that is larger than the group’s existing parity disk, then Data ONTAP reassigns the new disk as parity disk for that RAID group.
When an aggregate configured for RAID-DP protection is created, Data ONTAP assigns the role of dParity disk and regular parity disk to the largest and second largest disk in the RAID group.
When an existing RAID-DP group is assigned an additional disk that is larger than the group’s existing dParity disk, then Data ONTAP reassigns the new disk as the regular parity disk for that RAID group and restricts its capacity to be the same size as the existing dParity disk. Note that Data ONTAP does not replace the existing dParity disk, even if the new disk is larger than the dParity disk.

Note: Because the smallest parity disk limits the effective size of disks added to a RAID-DP group, you can maximize available disk space by ensuring that the regular parity disk is as large as the dParity disk.

Note: If needed, you can replace a capacity-restricted disk with a more suitable disk later, to avoid wasting disk space. However, you cannot increase the available disk space for existing disks by replacing a disk with a larger disk.

Example: adding a larger disk to a mixed-size RAID-DP aggregate

In this example, aggr2 has two 136-GB disks and one 68-GB disk. The 136-GB disks were used as the parity disks.

sys1> aggr status -r aggr2
Aggregate aggr2 (online, raid_dp) (block checksums)
  Plex /aggr2/plex0 (online, normal, active)
    RAID group /aggr2/plex0/rg0 (normal)

    RAID Disk    Device    HA   SHELF     BAY  CHAN     Pool     Type   RPM      Used (MB/blks)      Phys (MB/blks)
    ------------ --------- ---- --------  ---- -------- -------- ------ -------- ------------------ ----------------
    dparity      0c.48     0c   3         0    FC:A     -        FCAL   10000    136000/278528000   137104/280790184
    parity       0c.50     0c   3         2    FC:A     -        FCAL   10000    136000/278528000   137104/280790184
    data         0a.28     0a   1         12   FC:A     -        FCAL   10000     68000/139264000    69536/142410400

When another 136-GB disk is added to the aggregate, the disk is added as a data disk and is not restricted in size.

sys1> aggr add aggr2 -d 0c.49

sys1> aggr status -r aggr2
Aggregate aggr2 (online, raid_dp) (block checksums)
  Plex /aggr2/plex0 (online, normal, active)
    RAID group /aggr2/plex0/rg0 (normal)

    RAID Disk    Device    HA   SHELF     BAY  CHAN     Pool     Type   RPM      Used (MB/blks)     Phys (MB/blks)
    ------------ --------- ---- --------  ---- -------- -------- ------ -------- ------------------ ----------------
    dparity      0c.48     0c   3         0    FC:A     -        FCAL   10000    136000/278528000   137104/280790184
    parity       0c.50     0c   3         2    FC:A     -        FCAL   10000    136000/278528000   137104/280790184
    data         0a.28     0a   1         12   FC:A     -        FCAL   10000     68000/139264000    69536/142410400
    data         0c.49     0c   3         1    FC:A     -        FCAL   10000    136000/278528000   137104/280790184

Note: If the parity disk had been a 68-GB disk, then the newly added disk would have been restricted to 68 GB.

Parent topic: Increasing the size of an aggregate