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E-2 Recovering from Drive Failure
Problems such as reduced system performance or disk errors reported by the
operating system do not necessarily imply that a drive has or has not been failed.
If drive failures or repeated errors are suspected, Compaq recommends that
Drive Array Advanced Diagnostics be run on the system.
Fault Tolerance and Drive Failure
In the event of a drive failure, the condition of the logical drive will vary
depending upon the fault-tolerance method used. Since a single array of physical
drives can contain multiple logical drives with differing fault-tolerance methods,
conditions of each logical drive on the same array are not necessarily the same.
At any one time, if more drives are failed than the fault-tolerance mode allows,
fault tolerance is referred to as being "compromised" and the condition of the
logical drive can be referred to as "failed." If a logical volume is "failed," all
requests from the operating system will be rejected with "unrecoverable" errors.
A Non-Fault-Tolerant (RAID 0) Logical Drive
Can sustain no drive failures. If any physical drive in the array is failed,
the condition of all non-fault-tolerant logical drives in the same array
will also be "failed." This is because data is striped across all drives in
the array.
A RAID 1 (Mirroring) Logical Drive
Can sustain multiple drive failures as long as failed drives are not
mirrored to one another.
Will be in a "failed" condition if any two failed drives are mirrored to
one another.
Will be in a "regenerating" condition if at least one drive is failed, and
no failed drives are mirrored to one another.
Will be in a "rebuilding" condition if a previously failed drive has been
replaced and the replacement drive is rebuilding. The volume may also
be in a "rebuilding" condition following a drive failure if a spare drive
was previously assigned and is rebuilding.
Writer: Karen Hale Project: Compaq Smart Array 221 Controller User Guide Comments: 388541-001
File Name: M-APPE.DOC Last Saved On: 11/5/98 12:29 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
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