VA7410 performance when rebuilding

[Carl Houseman]

Have a VA7410 that recently lost a (73GB 15K)drive during business hours. It is set for all the defaults except RAID level is RAID1+0. And there is unallocated space equal to a single drive on each RG, so effectively two hot spares per RG.

While the array was rebuilding (rebuild priority: Low), performance of the RG with the failed drive was abysmal - maybe 10% of normal. Once the rebuild finished, performance returned to normal.

I've been told before that these arrays disable write caching when a battery is bad, accounting for terrible performance, but why would there be a similar loss of performance while rebuilding? There's no need for caching to be disabled.

I'm guessing I either need to config back to AutoRaid or set the rebuild priority to High, which couldn't possibly make performance worse. Can anyone say for sure the best solution?

thanks,
Carl