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09-21-2001 08:24 PM
09-21-2001 08:24 PM
va 7100 slow throughput
Hi - I have a new va7100 that's only showing around 35-50mb per second throughput. I used the following commands to verify this:
time dd if=/dev/rdsk/cXXXXX of=/dev/null 1024k count=50
This will read 50 MB off the disk device (you can set this to whatever value you want but 50 is sufficient for a good read test) and give you a time in seconds to do it.
eg.
50+0 records in
50+0 records out
Then divide 50 by whatever your time is to get mb / per second.
any thoughts on why this is running at below half of the advertised rate - things looked to be cabled correctly.
tx,
C
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09-23-2001 12:10 PM
09-23-2001 12:10 PM
Re: va 7100 slow throughput
Hi Charles:
Off the top of my head the maximum sustained rate is ~ 90MB/s. You don't mention what your host is, but it's rather difficult to push much beyond your observed rate through a single i/o channel. Glance will probably give you a better (more reliable) performance metric. I would also do your test with more than one server (or at least more than 1 dd).
You can save yourself a bit of clock watching by preceeding your dd command with 'timex'.
You might also want to create a /dev/zero device node (mknod /dev/zero c 3 0x000003) to serve as an input source to measure write rates.
Clay
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09-23-2001 11:09 PM
09-23-2001 11:09 PM
Re: va 7100 slow throughput
http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0xe85e46ff9277d511abcd0090277a778c,00.html
I recommend using in this discussion mentioned tool iozone to check performance.
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09-24-2001 09:42 AM
09-24-2001 09:42 AM
Re: va 7100 slow throughput
One more thought. At the very least your test is distorted by the time required to load dd and prepare it for execution. This overhead can be adjusted for by doing this command:
timex dd if=/dev/zero of=/dev/null bs=1024k count=50. This value can then be subtracted from your original dd command to give a somewhat better figure for the i/o rate.
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09-25-2001 04:49 AM
09-25-2001 04:49 AM
Re: va 7100 slow throughput
To help mitigate this behaviour, try using a different benchmark, or at least execute multiple dd's at the same time - 5 to 10 of them.
Good luck - I'm sure you'll see the 90MB/s if you do two things: use multiple dd's as I suggest, and use both controllers in the array (do the dd's over both channels).
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