[CentOS] 4.4/64-bit Supermicro/ Nvidia RAID [thanks]
Feizhou
feizhou at graffiti.net
Sat Dec 9 01:10:54 UTC 2006
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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