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Protecting Your Virtual Disk with a Hot Spare
Dell™OpenManage™ServerAdministratorStorageManagementUser'sGuide
Understanding Hot Spares
Considerations for Hot Spares on PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I, and CERC 6/I Controllers
Global Hot Spare Considerations on a SAS 6/iR
When you create a redundant virtual disk using a RAID controller, you have the opportunity to maintain system operations even when a disk fails. To do so,
you would assign a hot spare to the virtual disk. When a disk fails, the redundant data is rebuilt onto the hot spare without interrupting system operations.
Understanding Hot Spares
A hot spare is an unused backup physical disk that can be used to rebuild data from a redundant virtual disk. Hot spares remain in standby mode. When a
physical disk that is used in a redundant virtual disk fails, the assigned hot spare is activated to replace the failed physical disk without interrupting the system
or requiring your intervention. If a virtual disk using the failed physical disk is not redundant, then the data is permanently lost without any method (unless
you have a backup) to restore the data.
Hot spare implementation is different for different controllers. See the following sections for more information.
l "Considerations for Hot Spares on PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I, and CERC 6/I Controllers"
l "Global Hot Spare Considerations on a SAS 6/iR"
The following sections describe procedures for assigning a hot spare:
l "Assign and Unassign Global Hot Spare"
l "Assign and Unassign Dedicated Hot Spare"
Considerations for Hot Spares on PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I, and CERC
6/I Controllers
On the PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I, and CERC 6/I controllers, assigning a hot spare is equivalent to assigning a physical disk to replace another
physical disk if it fails. If more than one redundant virtual disk resides on the physical disk, then all redundant portions of the physical disk are rebuilt.
When creating a virtual disk, the physical disks included in the virtual disk can be different sizes. When assigning a hot spare to a RAID 1 or 5 virtual disk, the
hot spare only needs to be the same size (or larger) as the smallest physical disk included in the virtual disk.
This is because when using a PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I, and CERC 6/I controller, you can assign physical disks of different sizes to a virtual disk.
When you have fully consumed a smaller physical disk with a virtual disk, however, any portion of larger physical disks that are not consumed by the virtual
disk become unusable. Therefore, there is no data on the unused portion of a larger disk that needs to be rebuilt. A redundant virtual disk will also be either
striped or mirrored in equal portions across its member physical disks. The amount of data requiring a rebuild will therefore not be larger than the smallest
physical disk.
A RAID 10 or 50 virtual disk may include spans that have physical disks of different sizes. In this case, you should identify the span that has the largest "small"
physical disk. The hot spare should be large enough to rebuild this physical disk. For example, if one span has three physical disks that are 60 MB, 60 MB and
40 MB and another span has physical disks that are 60 MB, 60 MB, and 50 MB, then the hot spare must be 50 MB or larger.
A dedicated hot spare can only be assigned to the set of virtual disks that share the same physical disks. A global hot spare is assigned to all redundant
virtual disks on the controller. A global hot spare must be the same size (or larger) as the smallest physical disk included in any virtual disk on the controller.
After you have assigned a global hot spare, any new virtual disks created on the controller will not be protected by the hot spare if the controller is a SAS
controller and the disk size is larger than the global hot spare.
NOTE: When rebuilding a physical disk, you need to delete any nonredundant virtual disks (such as RAID 0) that reside on the physical disk before
rebuilding the physical disk.