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Introduction
Controlling Logical Unit States
The logical unit can be Online, Critical, or Offline. Note that the same term
"online" is used for both physical drives and logical units.
These states are defined as:
Controlling Standby Replacement Drives (Hot Spare)
The standby replacement drive (hot spare) is one of the most important features
in providing a high degree of fault-tolerance. With the standby rebuild function,
the controller performs a rebuild operation automatically when a disk drive fails
and both of the following conditions are true: a) a standby disk drive of identical
or larger capacity is found attached to the same controller, and b) all of the system
drives that are dependent on the failed disk are configured in a RAID 1, RAID 3,
RAID 5, or RAID 0+1 logical unit.
During the automatic rebuild process, system activity continues as normal.
System performance may degrade slightly, however, during a rebuild. Priority of
rebuild activity can be adjusted using the configuration utilities to adjust
performance versus rebuild time.
A standby replacement drive can be created in one of two ways: a) a disk may be
labeled a standby drive using the "Create Standby" option under the
Configuration menu using the VT100 option, or b) when the configuration is
created or changed using the software utility, any disks attached but not assigned
to a drive group will be automatically labeled as standby replacement drives.
10
Drive Management
Online – a logical unit has all of its participating physical drives on-line.
Critical – a logical unit has any of its physical drives not on-line. Note that in
a RAID 0 configuration, logical units are always in a critical state.
Offline – a logical unit is either:
a) it is configured with a redundant RAID level (1, 3, 5, 0+1) and two or
more of its drives are not on-line, and/or
b) it is configured as RAID 0 or JBOD and one or more of its drives is not
on-line.
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