Rebuild; Media Errors And Unreadable Sectors; Raid Operations And Features - Dell PowerVault MD3000 Hardware Owner's Manual

A hot spare may have the following states:
• 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.

Rebuild

If a disk fails in a fault-tolerant disk group (RAID 1, RAID 5, and RAID 10) and a hot spare is available,
the RAID software automatically attempts to rebuild the data to restore redundancy. If no hot spares are
available, an automatic rebuild occurs when a new physical disk is installed. You can use MD Storage
Manager to select a specific physical disk on which the rebuild should occur.
The requirements for a replacement physical disk are the same as those for a hot spare: the capacity
should be equal to or larger than the size of the configured capacity on the physical disk it replaces,
including its metadata.
NOTE:
For a stripe set of mirrors (RAID 10), it is possible for multiple disks to fail without a virtual disk failure.
NOTE:
If a bad block is encountered in any physical disks in the degraded disk groups during a rebuild, the disk
group fails and an automatic recovery procedure begins. For more information, see the MD Storage Manager
User's Guide.

Media Errors and Unreadable Sectors

If the RAID controller detects a media error while accessing data from a physical disk that is a member of
a disk group with a redundant RAID level (RAID 1, RAID 5 or RAID 10), the controller will try to recover
the data from peer disks in the disk group and will use recovered data to correct the error. If the controller
encounters an error while accessing a peer disk, it is unable to recover the data and affected sectors are
added to the unreadable sector log maintained by the controller.
Other conditions under which sectors are added to the unreadable sector log include:
• A media error is encountered when trying to access a physical disk that is a member of a non-
redundant disk group (RAID 0 or degraded RAID 1, RAID 5 or RAID 10).
• An error is encountered on source disks during rebuild.
NOTE:
Valid data on an unreadable sector is no longer accessible.

RAID Operations and Features

This section details the following RAID operations and features supported by your enclosure or RAID
controller:
• Virtual disk operations
• Disk group operations
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Using Your RAID Enclosure