Raid 5 performance

[The Edge of the Ice]

On Tue, 21 Sep 2004 16:16:49 -0400, Martin Duclos <tchitow-PkbjNfxxIARBDgjK7y7TUQ at public.gmane.org> wrote:
> The question is not really about what hardware configuration will make it
> better, rather, I want to know where to look to get nubmers. I want to know
> if the io is the bottleneck or if the cpu is the bottleneck. I'm not really
> interested in changing my setup. I am just curious as to ways I can monitor
> performance of that system in particular. BTW I have 4 ide controller as in
> a seperate cable for every drive.

vmstat is your friend, then.  You could also just use 'top' (btw, you
get a lot more information out of 'top' when running a 2.6 kernel). 
Hit the box with a workload, and see if your CPU is maxing out.  If
not, check to see if the ethernet interface is maxing out. (8MB/s is
about all you can squeeze out of a 100bT interface; I frequently get
closer to 4, but I havne't tweaked it).  Do doublecheck to make sure
that DMA is turned on for your HDs, as that makes it feasible (even if
not actually possible, I don't know) for a P120 to saturate all four
disks, versus being unable to saturate even one.  Also make sure that
the box is NOT SWAPPING.  If it is, more RAM is definitely on the
bill.  It's normal for all of RAM to be used (as cache), but if you're
using more than a few kilobytes of swap, you're probably getting
killed by the extra random disk accesses.

-- 
taa
/*eof*/
--
The Toronto Linux Users Group.      Meetings: http://tlug.ss.org
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://tlug.ss.org/subscribe.shtml