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Disk Rebuild
You rebuild a hard drive by recreating the data that had been stored on the drive before
the drive failed. Rebuilding can be done only in arrays with data redundancy, such as
RAID level 1.
IBM IDE automatically and transparently rebuilds failed drives with user-definable
rebuild rates. If a hot spare is available, the rebuild starts automatically when a drive fails.
Rebuilding can start automatically at boot up if the mirror drive is degraded and a spare is
available.
Note:If a hot spare is not available, the failed hard drive must be replaced with a new hard
drive so that the data on the failed drive can be rebuilt. The replacement hard drive
capacity must be greater than or equal to the failed drive it replaces.
Hot Spares
A hot spare is an extra, unused hard drive that is part of the RAID subsystem. It is usually
in standby mode, ready for service if a drive fails. Hot spares permit you to replace failed
array drives without system shutdown or user intervention.
IBM IDE implements automatic and transparent rebuilds using hot spare drives,
providing a high degree of fault tolerance and zero downtime. The IBM IDE BIOS
configurator allows you to specify physical drives as hot spares. When a hot spare is
needed, IBM IDE automatically selects the spare and includes it in the configuration.
Note that spare drives are applicable only in arrays with redundancy, such as RAID 1
arrays.
Check Consistency
In RAID, check consistency verifies the correctness of redundant data in an array and
helps to find disk errors. For example, in a system with a mirrored drive, checking
consistency means making sure that both the member-drives of the mirror contains the
same data.
Configuration Strategies
The most important factors in RAID array configuration are drive availability (fault
tolerance), and drive performance.
Maximizing Drive Availability You can maximize the drive availability by increasing fault tolerance. Use
RAID 1 or mirror configuration to attain this objective.
Maximizing Drive Performance You can optimize drive performance by using striping. Select RAID 0 or
striping to configure an array for optimal performance.
Performance and Availability You can achieve both drive performance and availability. Select RAID 10
for this configuration. You will need four drives to configure RAID 10.
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IBM ATA 133 RAID Controller User's Guide
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