How Data ONTAP works with hot spares
A hot spare disk is a disk that is assigned to a storage system but is not in use by a RAID group. It does not yet hold data but is ready for use. If a disk failure occurs within a RAID group, Data ONTAP automatically assigns hot spare disks to RAID groups to replace the failed disks.
- Hot spare best practices
At a minimum, you should have at least one matching or appropriate hot spare available for each kind of disk installed in your storage system. However, having two available hot spares for all disks is a best practice.
- What disks can be used as hot spares
A disk must conform to certain criteria to be used as a hot spare for a particular data disk.
- What a matching spare is
A matching hot spare exactly matches a data disk for several characteristics.
- What an appropriate hot spare is
If a disk fails and no hot spare disk that exactly matches the failed disk is available, Data ONTAP uses the best available spare.
- About degraded mode
When a disk fails, Data ONTAP can continue to serve data, but it must reconstruct the data from the failed disk using RAID parity. When this happens, the affected RAID group is said to be in degraded mode. The performance of a storage system with one or more RAID groups in degraded mode is decreased.
- About low spare warnings
By default, Data ONTAP issues warnings to the console and logs if you have fewer than one hot spare disk for each disk in your storage system. You can change the threshold value for these warning messages by using the raid.min_spare_count option.
