[linux-lvm] LVM on SATA/PATA disks

[Stuart D. Gathman]

On Sat, 12 May 2007, Bertrand Renuart wrote:

> I always have been told (S/P)ATA disks should somehow be avoided in server
> systems. This mainly because the high rate of interrupt requests generated
> by the IO subsystem will constantly interrupt the CPU which then becomes
> unavailable for other server tasks. SCSI disks should be preferred mainly
> for that reason.
> 
> Can someone confirm this statement?

The interrupt rate has nothing to do with the type of disk, and a lot to
do with the controller.  There is a CPU difference between $50 
consumer IDE/SATA adapters, and $300 server grade IDE/SATA adapters.
You'll want the controller to support fast DMA at minimum.

> FYI, we have to upgrade one of our development machine - hence the question.
> This machine is mainly used to run unattended software builds -> moves large
> quantity of small files and requires lots of CPU.

However, even the $50 adapters are way faster than what you could get
10 years ago.  I would start with a higher end $50+ adapter (you want
it reliable).  If you get a lot of "system" CPU time during heavy disk
IO, then the $300 adapter will relieve that.  For example, a super cheap
ATA adapter was giving us 25% system CPU on backups on a 1.8Ghz Celeron.
Replacing that with a more expensive (but < $100) IDE adapter reduced 
system time to 1% or so.

-- 
	      Stuart D. Gathman <stuart at bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
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