John R Pierce wrote:
Hardware raid is not necessarily faster than software raid.
hardware raid with battery-backed writeback cache is HUGELY faster at the very critical synchronous commit (fsync()) operations required by transactional database servers. so it all depends on what your application requirements are. if you just care about single threaded sequential reads, you'll probably do best with software SATA RAID10 on SATA. if you need fast random access committed writes, then you need a raid card with cache, and a battery so that you can safely enable writeback caching in the controller.
I contest the 'HUGELY faster' part. I won't contest that a 3ware RAID card can do mirroring better than Linux md even though md has improved in its handling of mirrors; it is not quite at the level of the 3ware RAID card but that does not mean it is faster except when doing rebuilds.
Fast random access committed writes like those of a mail queue happen to be my area of experience. It took a ten disk RAID array of SATA drives which just happened to be configured in RAID5 mode (not my idea) to get acceptable performance compared to 4 disk RAID10 md arrays.
I can accept faster in certain cases but if you say HUGELY faster, I would like to see some numbers.