[CentOS] 4.4/64-bit Supermicro/ Nvidia RAID [thanks]

Sat Dec 9 01:10:54 UTC 2006
Feizhou <feizhou at graffiti.net>

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.