Dell PowerVault MD3260 Administrator's Guide - Page 74

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 RAID level 5 or RAID level 6 Criteria for Enclosure Loss Protection 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. 74