How to translate disk i/os per second to throughput?

How to translate disk i/os per second to throughput?

Post by J.W. » Fri, 24 May 2002 02:49:46



When a vendor or spec sheet says a disk frame will do 65 i/os per
second, how do you translate that to megabytes per second?

For example, EMC says the disks should do 65 i/os per second and when
I do a "cp filename /dev/null" I get 5 megabytes per second transfer
throughput. Do these numbers correlate with each other?

Thanks for any advice.

 
 
 

How to translate disk i/os per second to throughput?

Post by Jeremiah DeWitt Weine » Sun, 26 May 2002 00:13:05


        I was waiting to see if anybody had any insightful answers,
but it appears not...


> When a vendor or spec sheet says a disk frame will do 65 i/os per
> second, how do you translate that to megabytes per second?

        You can't, unless every IO operation is the exact same size.
Also, that seems like a weird way to spec a disk.  Usually they're
touted in terms of bandwidth or throughput, not just IOs.

Quote:> For example, EMC says the disks should do 65 i/os per second and when
> I do a "cp filename /dev/null" I get 5 megabytes per second transfer
> throughput. Do these numbers correlate with each other?

        Not really.  Run "iostat -xnM 1" and see what you get.  Check this:

$ dd if=/dev/zero of=/var/tmp/JUNK bs=1 & iostat -xnM 1
                    extended device statistics              
    r/s    w/s   Mr/s   Mw/s wait actv wsvc_t asvc_t  %w  %b device
    0.0  160.0    0.0    0.1  0.0  0.0    0.0    0.3   0   4 c0t0d0

        Wow, 160 writes per second!  Clearly my disk is far better than
yours.  ;-)  However, note that the actual amount written to disk is
pathetically small.  Whereas...

$ dd if=/dev/zero of=/var/tmp/JUNK bs=1024k & iostat -xnM 1
                    extended device statistics              
    r/s    w/s   Mr/s   Mw/s wait actv wsvc_t asvc_t  %w  %b device
    0.0  126.5    0.0   13.8  4.4  2.0   34.5   15.8 100 100 c0t0d0

        Fewer writes per second, but much more data written to disk.
This is why operations is not a good benchmark.

--
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How to translate disk i/os per second to throughput?

Post by Darren Dunha » Sun, 26 May 2002 00:52:26



>    I was waiting to see if anybody had any insightful answers,
> but it appears not...

>> When a vendor or spec sheet says a disk frame will do 65 i/os per
>> second, how do you translate that to megabytes per second?
>    You can't, unless every IO operation is the exact same size.
> Also, that seems like a weird way to spec a disk.  Usually they're
> touted in terms of bandwidth or throughput, not just IOs.

Usually both are mentioned.

If you're doing sequential, large-block work, you'll max the
throughput.  If you're doing random, small-block work, you'll max the
I/Os before then.

Quote:>    Fewer writes per second, but much more data written to disk.
> This is why operations is not a good benchmark.

Depends on what you're doing...  For certain databases, it's more of a
limit than throughput is.

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Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
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+-[ Cameron Kerr ]--------------------------+

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