VA7100 RAID Allocations

[James Raffeld]

Thanks for the additional info about letting the array idle. Sunday after the my normal cold backup of oracle I will let the system sit and leave the db down and see if it will start optimizing.

[Roger_22]

Upgrade to HP18, keep current Resilience setting (Normal Mode), enable Pre-fetch. These are key to providing the best performance.

AutoRAID keeps the active write working set in RAID 1+0. These are the small (<256K from cache to the disks) IOs. Data that is not frequently written, or written with large blocks is kept in RAID 5DP.

The old Model 12H maximized RAID 1 space. But that proved to be a poor performance choice. As new data is written to the array, it must first create free space by converting some RAID 1+0 capacity to RAID 5 ??? this takes time, time that the new write must wait on. Also, without free space, the array could not do the highly efficient log-structured RAID 5 writes. The VA will optimize for free-space, but is also able to keep large amounts of data in RAID 1+0 for short periods.

If you created a new LUN and wrote randomly to the array and it created RAID 5DP capacity, then cache was able to concatenate the IOs into 256K records to the back end. These large-block writes are more efficient to the log-structured RAID 5DP than to RAID 1+0.