Disk Rebuilds - Lenovo ThinkServer RD330 Software User's Manual

MegaRAID SAS Software User Guide
2.4.13

Disk Rebuilds

Hot spare drives can be located on any RAID channel. Standby hot spares (not being
used in RAID drive group) are polled every 60 seconds at a minimum, and their status
made available in the drive group management software. RAID controllers offer the
ability to rebuild with a disk that is in a system, but not initially set to be a hot spare.
Observe the following parameters when using hot spares:
 Hot spares are used only in drive groups with redundancy: RAID levels 1, 5, 6, 10, 50,
and 60.
 A hot spare connected to a specific RAID controller can be used to rebuild a drive
that is connected to the same controller only.
 You must assign the hot spare to one or more drives through the controller BIOS or
use drive group management software to place it in the hot spare pool.
 A hot spare must have free space equal to or greater than the drive it replaces. For
example, to replace an 18-GB drive, the hot spare must be 18 GB or larger.
When a drive in a RAID drive group fails, you can rebuild the drive by recreating the
data that was stored on the drive before it failed. The RAID controller recreates the data
using the data stored on the other drives in the drive group. Rebuilding can be done
only in drive groups with data redundancy, which includes RAID 1, 5, 6, 10, 50, and 60
drive groups.
The RAID controller uses hot spares to rebuild failed drives automatically and
transparently, at user-defined rebuild rates. If a hot spare is available, the rebuild can
start automatically when a drive fails. If a hot spare is not available, the failed drive must
be replaced with a new drive so that the data on the failed drive can be rebuilt.
The failed drive is removed from the virtual drive and marked ready awaiting removal
when the rebuild to a hot spare begins. If the system goes down during a rebuild, the
RAID controller automatically restarts the rebuild after the system reboots.
NOTE: When the rebuild to a hot spare begins, the failed drive is often removed from
the virtual drive before management applications detect the failed drive. When this
occurs, the events logs show the drive rebuilding to the hot spare without showing the
failed drive. The formerly failed drive will be marked as "ready" after a rebuild begins to
a hot spare.
NOTE: If a source drive fails during a rebuild to a hot spare, the rebuild fails, and the
failed source drive is marked as offline. In addition, the rebuilding hot spare drive is
changed back to a hot spare. After a rebuild fails because of a source drive failure, the
dedicated hot spare is still dedicated and assigned to the correct drive group, and the
global hot spare is still global.
An automatic drive rebuild will not start if you replace a drive during a RAID-level
migration. The rebuild must be started manually after the expansion or migration
procedure is complete. (RAID-level migration changes a virtual drive from one RAID
level to another.)
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Chapter 2: Introduction to RAID Components and Features
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