HP StorageWorks Scalable File Share System Installation and Upgrade Guide Version 2.2

The configure array commandJ–8
J.7 Recommended RAID rebuild priority settings on SFS20 arrays
To reduce the possibility of data being lost during a RAID rebuild operation, HP recommends that the rebuild
priority is set to high on all SFS20 arrays that are configured with RAID 5 redundancy. (The configure
array command sets the rebuild_priority argument to high by default when an array is first
configured.)
Setting the rebuild priority to high prioritizes the RAID rebuild operation, and lowers the priority of host
requests; this means that the I/O performance on the array is heavily degraded during the time that the
RAID rebuild operation is in progress. As a result, when a disk is replaced, there is an initial period (during
the RAID rebuild operation) when the performance of the array is severely degraded. If the performance
degradation becomes an issue, you can reduce the impact of the RAID rebuild operation by setting the
rebuild_priority for the affected array to medium.
To set the rebuild_priority on an array, enter the following command on one of the servers attached
to the array:
sfs> set array 1 rebuild_priority=medium
The command may take a few minutes to complete.
Note the following points:
• On SFS20 arrays that are populated with 160GB or 250GB disks and configured with ADG
redundancy, if high performance during a RAID rebuild operation is critical, you can configure the
arrays with a rebuild priority of medium.
Because ADG redundancy can handle two disk failures, the risk of data loss during a RAID rebuild
operation is not as high as it is on arrays configured with RAID 5 redundancy.
• On SFS20 arrays that are populated with 500GB disks and configured with ADG redundancy, HP
recommends that the rebuild priority is set to high. This is because of the long rebuild time associated
with such disks.
• HP does not recommend using a rebuild priority of low for SFS20 arrays in any configuration.
For information on rebuilding metrics and the expected timing for RAID rebuild operations, refer to
Appendix D of the HP StorageWorks Scalable File Share System User Guide.