HP Compaq Integrated Smart Array Controller - Manual (Page 128)

B-22 Compaq Integrated Smart Array Controller User Guide
Compaq Confidential – Need to Know Required
Writer: CDresden Project: Compaq Integrated Smart Array Controller User Guide Comments:
Part Number: 153236-001 File Name: i-appb Understanding Drive Arrays.doc Last Saved On: 8/27/99 11:35 AM
Fault Tolerance and Drive Failure
In case of a drive failure, the condition of the logical drive will vary depending
upon the fault-tolerance method used. Because a single array of physical
drives can contain multiple logical drives with different 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 RAID 0 (Non-Fault-Tolerant) Logical Drive
Non-fault-tolerant logical drives cannot sustain drive failures. If any physical
drive in the array fails, the condition of all non-fault-tolerant logical drives in
the same array is also logged as “failed” because data is striped across all
drives in the array.
A RAID 1 (Mirroring) Logical Drive
RAID 1 logical drives:
■ 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.
■ In any RAID 1 logical drive on the Integrated Smart Array 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.