D-22
Understanding Drive Arrays
Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002
File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
Interim Data Recovery
In RAID 5, RAID 4, or RAID 1 fault-tolerant configurations, if a drive fails,
the system continues to operate in an interim data recovery mode. For
example, if you had selected RAID 5 for a logical drive with four physical
drives and one of the drives fails, the system continues to process I/O requests,
but at a reduced performance level. Replace the failed drive as soon as
possible to restore performance and full fault tolerance for that logical drive.
Refer to Appendix G for more information on recovering from drive failure.
Automatic Data Recovery
After you replace a failed drive, automatic data recovery reconstructs the data
and places it on the replaced drive. This allows a rapid recovery to full
operating performance without interrupting normal system operations.
In general, the time required for a rebuild is approximately 15 minutes per
gigabyte. The actual rebuild time however is dependent upon the rebuild
priority set for the amount of I/O activity occurring during the rebuild
operation and upon disk drive speed, and the number of drives in the array
(RAID 4 and RAID 5). In RAID 4 and RAID 5 configurations, the rebuild
time varies from 10 minutes/GB for three drives to 20 minutes/GB for 14
drives (using 9-GB wide-ultra hard drives).
NOTE
: You must specify RAID 5, RAID 4, or RAID 1 through the Array
Configuration Utility to make the recovery feature available. The drive failure
alert system and automatic data recovery are functions of the SMART-2DH
Controller; they operate independently of the operating system.