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RAID Availability
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.
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 rebuild 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 disk subsystem, a cold swap requires that you
power down the system.
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.
Copyback
The copyback feature allows you to copy data from a source drive of a virtual drive to a
destination drive that is not a part of the virtual drive. Copyback is often used to create or
restore a specific physical configuration for a drive group (for example, a specific arrangement
of drive group members on the device I/O buses). Copyback can be run automatically or
manually.
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Intel
RAID Software User's Guide
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