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.