Users guide

23 Intel® RAID Software User Guide
2.4 RAID Availability
2.4.1 RAID Availability Concept
Data availability without downtime is essential for many types of data processing and
storage systems. Businesses want to avoid the financial costs and customer frustration
associated with failed servers. RAID helps you maintain data availability and avoid
downtime for the servers that provide that data. RAID offers several features, such as
spare drives and rebuilds, that you can use to fix any physical disk problems, while
keeping the servers running and data available. The following subsections describe these
features.
2.4.2 Spare Drives
You can use spare drives to replace failed or defective drives in an array. A replacement
drive must be at least as large as the drive it replaces. Spare drives include hot swaps, hot
spares, and cold swaps.
A hot swap is the manual substitution of a replacement unit in a disk subsystem for a
defective one, where the substitution can be performed while the subsystem is running
(performing its normal functions). In order for the functionality to work, the backplane
and enclosure must support hot swap.
Hot-spare drives are physical drives that power up along with the RAID drives and
operate in a standby state. If a physical disk used in a RAID virtual disk fails, a hot spare
automatically takes its place and the data on the failed drive is rebuilt on the hot spare. Hot
spares can be used for RAID levels 1, IME, 5, 6, 10, 50, and 60.
Note: If a r
ebuild to a hot spare fails for any reason, the hot-spare drive will be marked as
“failed”. If the source drive fails, both the source drive and the hot-spare drive will be
marked as “failed”.
Before you replace a defective physical disk in a dis
k subsystem, a cold swap requires that
you power down the system.
2.4.3 Rebuilding
If a physical disk fails in an array that is configured as a RAID 1, IME, 5, 6, 10, 50, or 60
virtual disk, you can recover the lost data by rebuilding the drive. If you have configured
hot spares, the RAID controller automatically tries to use them to rebuild failed arrays. A
manual rebuild is necessary if there are no hot spares available with enough capacity to
rebuild the failed array. Before rebuilding the failed array, you must install a drive with
enough storage into the subsystem.