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quick disk performance test ?

 
Stuart Abramson
Trusted Contributor

quick disk performance test ?

I wanted to run a quick disk performance test, in response to questions that have come up.
I wrote this little script:
TIME=$(timex dd if=$Disk of=/dev/null count=10000 2>&1 \
| grep real | awk '{print $2}' )
print -n ${DISKA[$I]} "\t" $TIME "\t"
echo 5.12 $TIME | awk '{printf "%.2f\n", $1 / $2 }'
The idea is that I read raw 10000 blocks of block size 512 bytes = 5 MBs and then caclulate the MBytes/sec.
I'm not conducting a rigorous scientific test. I just want to have something to take to the performance group (who will make recommendations back to the UNIX and Storage teams).
Questions:
1. Does this sound reasonable?
2. Is a raw read off the rdsk acceptable for performance measurements? I compared it to a dd if=/dev/vgXX/lvolNN and it came out in the same range.
3. I'm getting values in the range of 2.8 MBytes/sec. Does that sound reasonable?

8 REPLIES 8
harry d brown jr
Honored Contributor

Re: quick disk performance test ?


What kind of disk drive?

Performance will be based upon speed of rotation (RPM's), IO interface speed, CPU availability, disk caching, ....

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harry d brown jr
Live Free or Die
Simon Hargrave
Honored Contributor

Re: quick disk performance test ?

This will give you a basic test however

- If you are testing a disk on an array (XP, EVA, EMC etc) then your results will be greatly skewed due to cache.

- You should perform the tests when the system is idle - random access to the disk you are testing again will skew the results.

Your 2.8MB/sec doesn't sound very fast, but it depends again on your server. On an rp54xx I'm getting about 8MB/sec on the internal 36Gb disks, but if you're testing an old A class for example those numbers may be more indicative.

You may be better using a combination of Glance/Measureware to get performance information with "real" data.
Alzhy
Honored Contributor

Re: quick disk performance test ?

I will do:

dd if=/dev/vgname/rlvolname of=/dev/null bs=1024k count=nnn

where nnnn should be sufficiently large to overcome the effect of cache.

Note, for LVM.. your RAW device is the lvolname prefixed with "r".

You may also do the same command on raw physical disks.. i.e. /dev/rdsk/cXtYdZ

I would prefer iozone though.
Hakuna Matata.
Stuart Abramson
Trusted Contributor

Re: quick disk performance test ?

They're EMC drives.
Cem Tugrul
Esteemed Contributor

Re: quick disk performance test ?

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=864715
Our greatest duty in this life is to help others. And please, if you can't
Cem Tugrul
Esteemed Contributor

Re: quick disk performance test ?

hi,
Please have a look my attachment

good Luck,
Our greatest duty in this life is to help others. And please, if you can't
Stuart Abramson
Trusted Contributor

Re: quick disk performance test ?

Several people told me that my blocksize for my reads was to small and that fixed me up.

I tried various blocksizes from 512 to 32768 and I/O rate increases from 2 MB/s to 45 MB/s (depending on server, disk, etc.). Block Size of 8192 gives me about 20-30 MB/s on hpux L3000s connected to EMC Symmetrix DMX 2000 with 2 Gb/s FAs:

((BS=8192))
((Count=5120000/BS))
TIME=$(timex dd if=$Disk of=/dev/null count=$Count bs=$BS 2>&1 \
| grep real | awk '{print $2}' )
MBpS=$( FDIV 5.12 $TIME )
printf "%5s %6s %8s %6s %6s %6s %6s \n" \
$LUN $ARRAY $DISK $SP $BS $TIME $MBpS

Re: quick disk performance test ?

Don't re-invent the wheel! There's plenty of free software out there that will do this kind of testing pretty easily - my personal favoutite is iozone:

http://www.iozone.org

But HP also have a bunch more listed here:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50460#N1053E


HTH

Duncan

I am an HPE Employee
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