Hot Spare Pools

A hot spare pool is an ordered list (collection) of hot spares.

You can place hot spares into one or more pools to get the most security from the fewest slices. Then, a hot spare pool can be assigned to any number of submirror metadevices or RAID5 metadevices.

You can assign a single hot spare pool to multiple submirrors or RAID5 metadevices. On the other hand, a submirror or a RAID5 metadevice can be associated with only one hot spare pool.

When errors occur, DiskSuite checks the hot spare pool for the first available hot spare whose size is equal to or greater than the size of the slice being replaced. If found, DiskSuite changes the hot spare's status to "In-Use" and automatically resyncs the data. In the case of a mirror, the hot spare is resynced with data from a good submirror. In the case of a RAID5 metadevice, the hot spare is resynced with the other slices in the metadevice. If a slice of adequate size is not found in the list of hot spares, the submirror or RAID5 metadevice that failed goes into an "errored" state. In the case of the submirror, it no longer replicates the data which that slice represented. In the case of the RAID5 metadevice, data redundancy is no longer available.

Hot Spare Pool Conventions

• How are hot spare pools named?

  Hot spare pools are named hspnnn, where nnn is in the range 000-999.

• What are "empty" hot spare pools?

  You can create empty hot spare pools, enabling you to add hot spares when they become available.

• How many hot spare pools are permitted?

  1000.

• Must a hot spare be a physical device?

  Yes. It cannot be a metadevice.

• How does the hot spare replacement algorithm work?

  When a slice in a submirror or RAID5 metadevice goes into the "errored" state, a slice from the associated hot spare pool is used to replace it. DiskSuite selects the first hot spare (slice) that is large enough to replace the errored slice.

  DiskSuite searches a hot spare pool for a hot spare based on the order in which hot spares are added to a hot spare pool. The first hot spare found that is large enough is used as a replacement. When adding hot spares to a hot spare pool, it is best to add them from smallest to largest. This avoids potentially wasting "large" hot spares as replacements for small slices.

• What are the size requirements for hot spares?

  Hot spares must be equal to or greater than the smallest slice in the submirror or RAID5 metadevice with which the hot spare pool is associated. If DiskSuite cannot substitute an appropriately sized hot spare for a failed slice in a submirror or RAID5 metadevice, hot sparing will not occur for that metadevice.

• Can a hot spare pool be associated with a "normal" stripe?

  No. Hot sparing can only be used for mirrors and RAID5 metadevices. A hot spare pool must be associated with a submirror or a RAID5 metadevice.

• What should I do if no hot spares are marked as Available?

  Some hot spares must be marked as Available. If all hot spares are marked In-Use, you should either add more hot spares to the hot spare pool or repair the spared slices and return them to service.

• Can I assign a hot spare pool to a one-way mirror?

  Do not assign a hot spare pool to a submirror in a one-way mirror. Failed slices in a one-way mirror cannot be replaced by a hot spare. In these metadevices, no other copy of data is available to reconstruct on the hot spare.

• Why should hot spares be defined on different controllers?

  To maximize their availability in case of controller errors or failures.