On Wed, 26 Sep 2007, Bryan J. Smith wrote:
Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
I wonder where the bottleneck lies.
The microcontroller.
Listen, for the last time, hardware RAID is _not_ for non-blocking
I/O. Hardware RAID is for in-line XOR streaming off-load, so it
doesn't tie up a system interconnect (which isn't an ideal use for
it).
I agree and this makes sense but in real-world loads it makes me wonder,
at least with the 2.4 kernel. I see hosts where total streaming does not
take place, instead lots of little files are copied on and off a host and
with the 2.4 kernel (RHEL3) the system 'feels' as if it were buried even
though the load is not that high ~9-10-15. Using ext3 on a 9 or 10 disk
RAID5 with default RAID parameters on a 3ware 9550SX card.
Justin.
A hardware RAID card is when you have other things going on in your
interconnect that you don't want the parity LOAD-XOR-STOR to take
away from what it could be using for the service.
It will _never_ have the "raw performance" of OS optimized software
RAID. At the same time, OS optimized software RAID's impact on the
system interconnect is one of those "unmeasurable" details _unless_
you actually benchmark your application.
I have repeatedly had issues with elementary UDP/IP NFS performance
when the PIO of software RAID is hogging the system interconnect.
Same deal for large numbers of large database record commits.
Understood.
--
Bryan J. Smith Professional, Technical Annoyance
b.j.smith@xxxxxxxx http://thebs413.blogspot.com
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Fission Power: An Inconvenient Solution
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