Dell PowerVault MD3820f - Manual (Page 100)

• A standby hot spare is a physical disk that has been assigned as a hot spare and is available to take
over for any failed physical disk.
• An in-use hot spare is a physical disk that has been assigned as a hot spare and is currently replacing a
failed physical disk.
Hot Spare Drive Protection
You can use a hot spare physical disk for additional data protection from physical disk failures that occur
in a RAID Level 1, or RAID Level 5 disk group. If the hot spare physical disk is available when a physical disk
fails, the RAID controller module uses redundancy data to reconstruct the data from the failed physical
disk to the hot spare physical disk. When you have physically replaced the failed physical disk, a copyback
operation occurs from the hot spare physical disk to the replaced physical disk. If there are secure disk
groups and security capable disk groups in the storage array, the hot spare physical disk must match the
security capability of the disk group. For example, a non-security capable physical disk cannot be used as
a hot spare for a secure disk group.
NOTE: For a security capable disk group, security capable hot spare physical disks are preferred. If
security capable physical disks are not available, non-security capable physical disks may be used as
hot spare physical disks. To ensure that the disk group is retained as security capable, the non-
security capable hot spare physical disk must be replaced with a security capable physical disk.
If you select a security capable physical disk as hot spare for a non-secure disk group, a dialog box is
displayed indicating that a security capable physical disk is being used as a hot spare for a non-secure
disk group.
The availability of enclosure loss protection for a disk group depends on the location of the physical disks
that comprise the disk group. The enclosure loss protection might be lost because of a failed physical
disk and location of the hot 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 below.
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.
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