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

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Drawer loss protection

In expansion enclosures that contain drawer-based physical disks, a drawer failure can prevent access to data on the virtual disks of a disk group.

Drawer loss protection for a disk group is based on the location of the physical disks that comprise the disk group. If there is a single drawer failure, data on the virtual disks in a disk group remains accessible if drawer loss protection configuration is followed. In such as case, if a drawer fails and the disk group is protected, the disk group changes to Degraded status and the data remains accessible.

Table 1. Drawer loss protection requirements for different raid levelsTo configure your storage for drawer loss protection, make sure that physical disks that are part of a disk group are located in different drawers regarding their RAID levels, as shown in the following table:
RAID Level Drawer Loss Protection Requirements
RAID Level 6 RAID Level 6 requires a minimum of 5 physical disks. Place all the physical disks in different drawers or place a maximum of two physical disks in the same drawer and the remaining physical disks in different drawers.
RAID Level 5 RAID Level 5 requires a minimum of 3 physical disks. Place all the physical disks in different drawers for a RAID Level 5 disk group. Drawer loss protection cannot be achieved for RAID Level 5 if more than one physical disk is placed in the same drawer.
RAID Level 1 and RAID Level 10 RAID Level 1 requires a minimum of 2 physical disks. Make sure that each physical disk in a remotely replicated pair is located in a different drawer. By locating each physical disk in a different drawer, you can have more than two physical disks of the disk group within the same drawer. For example, if you create a RAID Level 1 disk group with six physical disks (three replicated pairs), you can achieve the drawer loss protection for the disk group with only two drawers as shown in this example: 6-physical disk RAID Level 1 disk group:

Replicated pair 1 = Physical disk located in enclosure 1, drawer 0, slot 0, and physical disk in enclosure 0, drawer 1, slot 0

Replicated pair 2 = Physical disk in enclosure 1, drawer 0, slot 1, and physical disk in enclosure 1, drawer 1, slot 1

Replicated pair 3 = Physical disk in enclosure 1, drawer 0, slot 2, and physical disk in enclosure 2, drawer 1, slot 2

RAID Level 10 requires a minimum of 4 physical disks. Make sure that each physical disk in a remotely replicated pair is located in a different drawer.
RAID Level 0 You cannot achieve drawer loss protection because the RAID Level 0 disk group does not have consistency.
NOTE: If you create a disk group using the Automatic physical disk selection method, MD Storage Manager attempts to choose physical disks that provide drawer loss protection. If you create a disk group by using the Manual physical disk selection method, you must use the criteria that are specified in the previous table.

If a disk group already has a Degraded status due to a failed physical disk when a drawer fails, drawer loss protection does not protect the disk group. The data on the virtual disks becomes inaccessible.

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