Global Revertible Hot Spare
To achieve the best reliability and manageability, Promise recommends configuring all of the spares as global
revertible hot spares. The advantage of global revertible hot spares is that each of the hot spares can be used for
rebuilding the same logical drive or different logical drives, in the same enclosure or in different enclosures. Therefore,
when there are unevenly distributed drive issues, there are still enough hot spares to provide coverage and to allow RAID
redundancy to be restored in the shortest time frame.
As revertible spares, when the rebuild completes and the failed drive is replaced with a new drive, the used spare will
automatically be freed up and become a revertible spare again after the reversion process, called Transition, initiates and
completes in the background.
Due to reliability considerations, Promise does not recommend mixing drives from different enclosures in the same
disk array. Therefore, when a rebuild completes through using a hot spare from a different enclosure, Promise
recommends replacing the failed drive as soon as possible. When the new drive is inserted, Transition will start
automatically in the background. Eventually, the disk array will consist of drives in the same enclosure again.
The follow diagram illustrates how global revertible hot spares work.
Figure 4. How global revertible hot spares work
Enclosure 1 - E610f
Enclosure 2 - J610s
Enclosure 2, PD1 and PD2 failed.
Enclosure 1 - E610f
Enclosure 2 - J610s
Rebuild instantly kicked in
automatically using Enclosure
2 PD16 and Enclosure 1 PD16.
After rebuild completed, the
disk array 2 became crossing
enclosure 1 and 2.
Enclosure 2 PD1 and PD2 were
replaced with new drives.
Transition instantly kicked in
automatically.
When Transition completed, the new
drives became part of disk array 2, and
Enclosure 1 and Enclosure 2 PD16 were
reverted back to hot spare.
The configuration recovered exactly
the same as the original stage
Enclosure 1 - E610f
Enclosure 2 - J610s
Assuming using RAID 6 configuration.
Everything started out optimal condition.
Stage 1
Stage 2
Stage 3
As illustrated in Figure 4, global revertible hot spares ensure overall system reliability in case of drive failure. In addition,
they also facilitate management by enabling the entire rebuild and Transition process to be automated. Once the process
completes, the system is restored to its original state.
Logical Drive Attributes
To achieve the best performance, Promise recommends configuring each of the logical drives with the attribute values as
listed in the table below:
Best Practices Guide 9
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