134 Configuration: Disk Groups and Virtual Disks
spare physical disk. To make sure that enclosure loss protection is not
affected, you must replace a failed physical disk to initiate the copyback
process.
The virtual disk remains online and accessible while you are replacing the
failed physical disk, because the hot spare physical disk is automatically
substituted for the failed physical disk.
Enclosure Loss Protection
Enclosure loss protection is an attribute of a disk group. Enclosure loss
protection guarantees accessibility to the data on the virtual disks in a disk
group if a total loss of communication occurs with a single expansion
enclosure. An example of total loss of communication may be loss of power to
the expansion enclosure or failure of both RAID controller modules.
CAUTION: Enclosure loss protection is not guaranteed if a physical disk has
already failed in the disk group. In this situation, losing access to an expansion
enclosure and consequently another physical disk in the disk group causes a
double physical disk failure and loss of data.
Enclosure loss protection is achieved when you create a disk group where all
of the physical disks that comprise the disk group are located in different
expansion enclosures. This distinction depends on the RAID level. If you
choose to create a disk group by using the Automatic method, the software
attempts to choose physical disks that provide enclosure loss protection. If
you choose to create a disk group by using the Manual method, you must use
the criteria specified in Table 10-2.
Table 10-2. Criteria for Enclosure Loss Protection
RAID Level Criteria for Enclosure Loss Protection
RAID level 5
or RAID level
6
Ensure that all the physical disks in the disk group are located in
different expansion enclosures.
Because a RAID level 5 requires a minimum of 3 physical disks,
enclosure loss protection cannot be achieved if your storage array has
less than 3 expansion enclosures.
Because a RAID level 6 requires a minimum of 5 physical disks,
enclosure loss protections cannot be achieved if your storage array has
less than 5 expansion enclosures.
book.book Page 134 Tuesday, September 27, 2011 3:13 PM
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