[kwlug-disc] MDADM and RAID

Raul Suarez rarsa at yahoo.com
Tue Mar 2 12:04:22 EST 2010


Have you tried the hdparm or bonnie++ commands?

Raul Suarez

Technology consultant
Software, Hardware and Practices
_________________
http://rarsa.blogspot.com/ 
An eclectic collection of random thoughts


--- On Tue, 3/2/10, Chris Irwin <chris at chrisirwin.ca> wrote:

> From: Chris Irwin <chris at chrisirwin.ca>
> Subject: Re: [kwlug-disc] MDADM and RAID
> To: "KWLUG discussion" <kwlug-disc at kwlug.org>
> Received: Tuesday, March 2, 2010, 11:52 AM
> On Tue, Mar 2, 2010 at 08:05, Lori
> Paniak <ldpaniak at fourpisolutions.com>
> wrote:
> > What kind of hardware are you running on?  Software
> RAID 5 is going to
> > require a non-trivial amount of CPU power to do the
> parity calcs.  What
> > do 'top' and 'free' say?
> 
> My processor is an AMD Athlon 64 X2 4600+. That translates
> to 2.4GHz
> 64-bit processor. I'm running 64-bit Ubuntu 9.10 on it. I
> have 4GB
> RAM, free -m reports I have 2GB free. I ran some tests
> below. I'm not
> sure how to do some really objective disk tests, but am
> open to
> suggestion.
> 
> During this time I was watching top. dd used 50% CPU (which
> I believe
> means it is 50% of one core, i.e. not maxing out a
> processor). When it
> ran sync, a process called "md1_raid5" used up to 25% cpu.
> The machine
> is otherwise idle at the moment.
> 
> My unscientific test command was the following:
> 
> for i in $(seq 1 5); do
>   sync;
>   echo -e "\n===Iteration ${i}===";
>   time $( dd bs=1M count=500 if=/dev/zero
> of=/home/chris/zero; sync );
> done
> 
> For my raid5 test, I wrote to my home, which is on that
> array. For my
> non-raid comparison (non-raid disk plugged into same
> controller) I
> wrote to where that was mounted. Both are ext4 filesystems.
> I averaged
> the 'real' time over the five runs.
> 
> raid5 gives: 12.232
> bare disk gives: 6.8586
> 
> Now I'm not expecting miracles and I'm willing to take a
> performance
> hit to spare the cost of a dedicated raid controller, but
> is 50%
> throughput really the norm for raid5 with mdadm? And that
> is just with
> this simple test, I experienced much worse than 50%
> throughput with my
> lvm migration....
> 
> For anybody who is curious, here is the raw output from my
> tests:
> 
> [chris at jupitertwo:~]$ for i in $(seq 1 5); do sync; echo
> -e
> "\n===Iteration ${i}==="; time $( dd bs=1M count=500
> if=/dev/zero
> of=/home/chris/zero; sync ); done
> 
> ===Iteration 1===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.25245 s, 419 MB/s
> 
> real    0m11.135s
> user    0m0.010s
> sys     0m3.430s
> 
> ===Iteration 2===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.26102 s, 416 MB/s
> 
> real    0m11.994s
> user    0m0.000s
> sys     0m4.710s
> 
> ===Iteration 3===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.1752 s, 446 MB/s
> 
> real    0m12.962s
> user    0m0.010s
> sys     0m5.180s
> 
> ===Iteration 4===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.16783 s, 449 MB/s
> 
> real    0m12.707s
> user    0m0.010s
> sys     0m5.160s
> 
> ===Iteration 5===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.16648 s, 449 MB/s
> 
> real    0m12.362s
> user    0m0.000s
> sys     0m4.710s
> 
> 
> [chris at jupitertwo:~]$ for i in $(seq 1 5); do sync; echo
> -e
> "\n===Iteration ${i}==="; time $( dd bs=1M count=500
> if=/dev/zero
> of=/mnt/backup/chris/zero; sync ); done
> 
> ===Iteration 1===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.14573 s, 458 MB/s
> 
> real    0m6.909s
> user    0m0.000s
> sys     0m4.240s
> 
> ===Iteration 2===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.24725 s, 420 MB/s
> 
> real    0m6.886s
> user    0m0.010s
> sys     0m4.350s
> 
> ===Iteration 3===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.20556 s, 435 MB/s
> 
> real    0m6.856s
> user    0m0.000s
> sys     0m4.480s
> 
> ===Iteration 4===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.11238 s, 471 MB/s
> 
> real    0m6.663s
> user    0m0.000s
> sys     0m4.370s
> 
> ===Iteration 5===
> 500+0 records in
> 500+0 records out
> 524288000 bytes (524 MB) copied, 1.25068 s, 419 MB/s
> 
> real    0m6.979s
> user    0m0.000s
> sys     0m4.530s
> 
> 
> -- 
> Chris Irwin
> <chris at chrisirwin.ca>
> 
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