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.
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