Re: Re: mkfs options for a 16x hw raid5 and xfs (mostly large files)

["Bryan J. Smith" <thebs413@yahoo.com>]

Justin Piszcz <jpiszcz@lucidpixels.com> 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).

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.


-- 
Bryan J. Smith   Professional, Technical Annoyance
b.j.smith@ieee.org    http://thebs413.blogspot.com
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     Fission Power:  An Inconvenient Solution