Hot Spares - Lenovo ThinkServer RD650 User Manual

12Gb/s MegaRAID SAS Software User Guide
March 2014
Table 3 Spanning for RAID 10, RAID 50, and RAID 60
Level
00
10
50
60
2.1.12

Hot Spares

A hot spare is an extra, unused drive that is part of the disk subsystem. It is usually in Standby mode, ready for service
if a drive fails. Hot spares permit you to replace failed drives without system shutdown or user intervention. MegaRAID
SAS RAID controllers can implement automatic and transparent rebuilds of failed drives using hot spare drives,
providing a high degree of fault tolerance and zero downtime.
The RAID management software allows you to specify drives as hot spares. When a hot spare is needed, the RAID
controller assigns the hot spare that has a capacity closest to and at least as great as that of the failed drive to take the
place of the failed drive. The failed drive is removed from the virtual drive and marked ready awaiting removal after
the rebuild to a hot spare begins. You can make hot spares of the drives that are not in a RAID virtual drive.
You can use the RAID management software to designate the hot spare to have enclosure affinity, meaning that if
drive failures are present on a split backplane configuration, the hot spare will be used first on the backplane side in
which it resides.
If the hot spare is designated as having enclosure affinity, it attempts to rebuild any failed drives on the backplane in
which it resides before rebuilding any other drives on other backplanes.
The hot spare can be of two types:
Global hot spare

Dedicated hot spare

Global Hot Spare
Use a global hot spare drive to replace any failed drive in a redundant drive group as long as its capacity is equal to or
larger than the coerced capacity of the failed drive. A global hot spare defined on any channel should be available to
replace a failed drive on both channels.
Dedicated Hot Spare
Use a dedicated hot spare to replace a failed drive only in a selected drive group. One or more drives can be
designated as a member of a spare drive pool. The most suitable drive from the pool is selected for failover. A
dedicated hot spare is used before one from the global hot spare pool.
Configure RAID 00 by spanning two contiguous RAID 0 virtual drives, up to the maximum number of
supported devices for the controller.
Configure RAID 10 by spanning two contiguous RAID 1 virtual drives, up to the maximum number of
supported devices for the controller. RAID 10 supports a maximum of 8 spans. You must use an even number of
drives in each RAID virtual drive in the span. The RAID 1 virtual drives must have the same stripe size.
Configure RAID 50 by spanning two contiguous RAID 5 virtual drives. The RAID 5 virtual drives must have the
same stripe size.
Configure RAID 60 by spanning two contiguous RAID 6 virtual drives. The RAID 6 virtual drives must have the
same stripe size.
NOTE In a spanned virtual drive (R10, R50, R60) the span numbering starts
from Span 0, Span 1, Span 2, and so on.
NOTE If a rebuild to a hot spare fails for any reason, the hot spare drive is
marked as failed. If the source drive fails, both the source drive and the
hot spare drive are marked as failed.
Description
LSI Corporation
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Chapter 2: Introduction to RAID
Components and Features