Hot Spare Disks - IBM N Series Hardware Manual

RAID-DP volume management
From a management and operational point of view, RAID-DP aggregates and traditional
volumes work exactly like their RAID4 counterparts. The same practices and guidelines work
for both RAID4 and RAID-DP. Therefore, little to no changes are required for standard
operational procedures used by IBM System Storage N series administrators. The commands
you use for management activities on the storage controller are the same regardless of the
mix of RAID4 and RAID-DP aggregates or traditional volumes. For instance, to add additional
capacity, run the command [aggr | vol] add name X just as you would for a RAID4-based
storage.

10.5 Hot spare disks

A hot spare disk is a storage system disk that has not been assigned to a RAID group. It does
not yet hold data, but is ready for use. In a disk failure within a RAID group, Data ONTAP
automatically assigns hot spare disks to RAID groups to replace the failed disks.
Hot spare disks do not have to be in the same disk shelf as other disks of a RAID group to be
available to a RAID group (Figure 10-27).
Figure 10-27 RAID-DP protection
Tip: You need at least one spare disk available per aggregate, but no more than three. In
addition, the available spares need at least one disk for each disk size and disk type
installed in your storage system. This configuration allows the storage system to use a disk
of the same size and type as a failed disk when reconstructing a failed disk. If a disk fails
and a hot spare disk of the same size is not available, the storage system uses a spare
disk of the next available size up.
During disk failure, the storage system replaces the failed disk with a spare and reconstructs
data. If a disk fails, the storage system runs these actions:
1. The storage system replaces the failed disk with a hot spare disk. If RAID-DP is enabled
and double-disk failure occurs in the RAID group, the storage system replaces each failed
disk with a separate spare disk. Data ONTAP first attempts to use a hot spare disk of the
same size as the failed disk. If no disk of the same size is available, Data ONTAP replaces
the failed disk with a spare disk of the next available size up.
RAID-DP Protection
Vol_1
rg0
rg1
rg2
rg3
hot spare
Data drive
Parity drive
dParity drive
RAID group
Chapter 10. Data protection with RAID Double Parity
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