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In any RAID 1 logical drive on the Smart Array 221 Controller having N
physical drives in the array (not including spare drives), the first N/2
physical drives are normally mirrored in consecutive order to the second
N/2 physical drives. When determining the order, number each drive in
the array by increasing IDs on the SCSI bus.
A RAID 5 (Distributed Data Guarding) Logical
Drive
Can sustain a single drive failure. The logical drive will be in a
"regenerating" condition if one drive is failed.
Will be in a "failed" condition if more than one drive is failed.
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.
Spare Drives
In the event of a drive failure, if a spare drive is assigned and available, the
spare drive acts as an immediate replacement for the failed drive. Data is
automatically reconstructed from the remaining drive(s) in the volume and
written to the spare drive via the Automatic Data Recovery process. Once the
spare drive is completely built, the logical drive is again running at full fault-
tolerance, and is then able to sustain another subsequent drive failure. Note,
however, that if another drive were to fail before the spare drive is completely
built, the spare drive cannot prevent failure of the entire logical drive. Also note
that it is also possible for non-correctable disk errors to prevent completion of
the Automatic Data Recovery process (discussed below).
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
Compaq Smart Array 221 Controller User Guide
E-3
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