Spare Drives; Replacing A Failed Drive - Compaq RAID Array 4100 User Manual

In any RAID 1 logical drive on the RA4100 having N physical drives in the
array (not including spare drives), the first N/2 physical drives are 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 first SCSI bus,
followed likewise by drives on the second SCSI bus.
I
Can sustain a single drive failure. The logical drive will be in a
regenerating condition if one drive is failed.
I
Will be in a failed condition if more than one drive is failed.
I
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, it acts
as an immediate replacement for the failed drive. Data is automatically
reconstructed from the remaining drives 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.

Replacing a Failed Drive

Failed drives in hot-pluggable trays can be removed and replaced while host
system and storage system powers are both on. Of course, hot-pluggable
drives can also be replaced when the power is off. Remember, however, to
NEVER TURN OFF the RA4100 while the host system power is on. This
would result in the failure of all drives in the storage system, which would
likely compromise your fault tolerance. When a hot-pluggable drive is
inserted, all disk activity on the controller will be temporarily paused while the
drive is spinning up (usually 20 seconds or so). If the drive is inserted while
power is on, in fault tolerant configurations, recovery of data on the
replacement drive will automatically begin (indicated by a blinking
online LED).
The capacity of replacement drives must be at least as large as the capacity of
the other drives in the array. Drives of insufficient capacity will immediately
be failed by the controller without starting Automatic Data Recovery.
Recovering From Hard Drive Failure F-3