Dell PowerVault ME5 Series Administrator's Guide

Spares

Spare disks are unused disks in your system that automatically replace a failed disk, restoring fault tolerance to disk groups in the system. Designate spares from the Maintenance > Storage panel or by using the add spares CLI command. For information about this command, see the CLI Reference Guide.

Types of spares include:

• Dedicated spare—Reserved for use by a specific linear disk group to replace a failed disk. Most secure way to provide spares for disk groups, but it is expensive to reserve a spare for each disk group.
• Global spare—Reserved for use by any fault-tolerant disk group to replace a failed disk.
• Dynamic spare—Available compatible disk that is automatically assigned to replace a failed disk in a fault-tolerant disk group.

A controller automatically reconstructs a fault-tolerant disk group (RAID 1, 5, 6, 10) when one or more of its disks fails and a compatible spare disk is available. A disk is compatible if it has enough capacity to replace the failed disk and is the same type (enterprise SAS, for example). If the disks in the system are FDE-capable and the system is secure, spares must also be FDE-capable.

When a disk fails, the system looks for a dedicated spare first. If it does not find a dedicated spare, it looks for a global spare. If it does not find a compatible global spare and the dynamic spares option is enabled, it takes any available compatible disk. If no compatible disk is available, reconstruction cannot start.

On a 5U84 enclosure, the system first looks for spares in the same drawer as the failed disk, then in another drawer in the same enclosure, and then in another enclosure within the same system.