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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 3/SC, 3/DC, 3/QC, 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, 4e/Di, CERC ATA100/4ch, PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I,
and CERC 6/I Controllers
Considerations for Hot Spares on PERC 3/Si, 3/Di, CERC SATA1.5/6ch, S100, and S300 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 3/SC, 3/DC, 3/QC, 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, 4e/Di, CERC ATA100/4ch, PERC 5/E, PERC 5/i, PERC 6/E, PERC
6/I, and CERC 6/I Controllers"
l "Considerations for Hot Spares on PERC 3/Si, 3/Di, CERC SATA1.5/6ch, S100, and S300 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 3/SC, 3/DC, 3/QC, 4/SC, 4/DC, 4e/DC, 4/Di,
4e/Si, 4e/Di, CERC ATA100/4ch, PERC 5/E, PERC 5/i, PERC 6/E, PERC 6/I, and CERC
6/I Controllers
On the PERC 3/SC, 3/DC, 3/QC, 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, 4e/Di, CERC ATA100/4ch, 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 3/SC, 3/DC, 3/QC, 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, 4e/Di, CERC ATA100/4ch, 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 in either of the following
circumstances:
l The controller is a SCSI controller and the partition size of the disk is larger than the global hot spare.
l The controller is a SAS controller and the disk size is larger than the global hot spare.
In this case, you can unassign the global hot spare after creating a new virtual disk and then assign a new and larger hot spare to cover all redundant virtual
disks on the controller. See "RAID Controller Technology: SCSI, SATA, ATA, and SAS" to determine whether the controller is using SCSI or SAS technology.
On the PERC 3/SC, 3/DC, 3/QC, 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, 4e/Di, and CERC ATA100/4ch controllers, the virtual disk state is not updated until the controller
performs an I/O operation. This means that when a redundant virtual disk is degraded on one of these controllers, the hot spare will not be activated until the
controller performs an I/O operation. See "I/O and Reboot Requirements for Detecting Physical Disk Status Changes" for more information.
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.