Dell EMC PowerVault MD 34XX/38XX Series Storage Arrays Administrator's Guide

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.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.

Because a RAID level 5 requires a minimum of three physical disks, enclosure loss protections cannot be achieved if your storage array has less than three expansion enclosures. Because a RAID level 6 requires a minimum of five physical disks, enclosure loss protections cannot be achieved if your storage array has less than five expansion enclosures.

RAID level 1

Ensure that each physical disk in a replicated pair is located in a different expansion enclosure. This enables you to have more than two physical disks in the disk group within the same expansion enclosure.

For example, if you are creating a six physical disk, disk group (three-replicated pairs), you could achieve enclosure loss protection with only two expansion enclosures by specifying that the physical disk in each replicated pair are located in separate expansion enclosures. This example shows this concept:

• Replicate pair 1 — Physical disk in enclosure 1 slot 1 and physical disk in enclosure 2 slot 1.
• Replicate pair 2 — Physical disk in enclosure 1 slot 2 and physical disk in enclosure 2 slot 2.
• Replicate pair 3 — Physical disk in enclosure 1 slot 3 and physical disk in enclosure 2 slot 3.

Because a RAID level 1 disk group requires a minimum of two physical disks, enclosure loss protections cannot be achieved if your storage array has less than two expansion enclosures.

RAID level 0

Because RAID level 0 does not have consistency, you cannot achieve enclosure loss protection.