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Drive procedures 83
If you insert a hot-pluggable drive into a drive bay while the system power is on, all disk activity in the array
pauses for 1 or 2 seconds while the new drive is initializing. When the drive is ready, data recovery to the
replacement drive begins automatically if the array is in a fault-tolerant configuration.
If you replace a drive belonging to a fault-tolerant configuration while the system power is off, a POST
message appears when the system is next powered up. This message prompts you to press the F1 key to start
automatic data recovery. If you do not enable automatic data recovery, the logical volume remains in a
ready-to-recover condition and the same POST message appears whenever the system is restarted.
Before replacing drives
• Open Systems Insight Manager, and inspect the Error Counter window for each physical drive in the
same array to confirm that no other drives have any errors. For more information, see the Systems
Insight Manager documentation on the Management CD.
• Be sure that the array has a current, valid backup.
• Confirm that the replacement drive is of the same type as the degraded drive (either SAS or SATA and
either hard drive or solid state drive).
• Use replacement drives that have a capacity equal to or larger than the capacity of the smallest drive
in the array. The controller immediately fails drives that have insufficient capacity.
In systems that use external data storage, be sure that the server is the first unit to be powered down and the
last unit to be powered up. Taking this precaution ensures that the system does not, erroneously, mark the
drives as failed when the server is powered up.
In some situations, you can replace more than one drive at a time without data loss. For example:
• In RAID 1+0 configurations, drives are mirrored in pairs. You can replace several drives simultaneously
if they are not mirrored to other removed or failed drives.
• In RAID 50 configurations, drives are arranged in parity groups. You can replace several drives
simultaneously, if the drives belong to different parity groups. If two drives belong to the same parity
group, replace those drives one at a time.
• In RAID 6 configurations, you can replace any two drives simultaneously.
• In RAID 60 configurations, drives are arranged in parity groups. You can replace several drives
simultaneously, if no more than two of the drives being replaced belong to the same parity group.
To remove more drives from an array than the fault tolerance method can support, follow the previous
guidelines for removing several drives simultaneously, and then wait until rebuild is complete (as indicated by
the drive LEDs) before removing additional drives.
However, if fault tolerance has been compromised, and you must replace more drives than the fault tolerance
method can support, delay drive replacement until after you attempt to recover the data (refer to "Recovering
from compromised fault tolerance" on page 82).
Automatic data recovery (rebuild)
When you replace a drive in an array, the controller uses the fault-tolerance information on the remaining
drives in the array to reconstruct the missing data (the data that was originally on the replaced drive) and
then write the data to the replacement drive. This process is called automatic data recovery or rebuild. If fault
tolerance is compromised, the controller cannot reconstruct the data, and the data is likely lost permanently.