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SubjectRe: Poor performance during disk writes


On Tue, 18 Dec 2001, Andre Hedrick wrote:

> File './Bonnie.2276', size: 1073741824, volumes: 1
> Writing with putc()... done: 72692 kB/s 83.7 %CPU
> Rewriting... done: 25355 kB/s 12.0 %CPU
> Writing intelligently...done: 103022 kB/s 40.5 %CPU
> Reading with getc()... done: 37188 kB/s 67.5 %CPU
> Reading intelligently...done: 40809 kB/s 11.4 %CPU
> Seeker 2...Seeker 1...Seeker 3...start 'em...done...done...done...
> ---Sequential Output (nosync)--- ---Sequential Input-- --Rnd Seek-
> -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --04k (03)-
> Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
> 1*1024 72692 83.7 103022 40.5 25355 12.0 37188 67.5 40809 11.4 382.1 2.4
>
> Maybe this is the kind of performance you want out your ATA subsystem.
> Maybe if I could get a patch in to the kernels we could all have stable
> and fast IO.

I rather see lots of wasting rather than performance, here. Bonnie says
that your subsystem can sustain 103 MB/s write but only 41 MB/s read. This
looks about 60% throughput wasted for read.

Note that if you intend to use it only for write-only applications,
performance are not that bad, even if just dropping the data on the floor
would give you infinite throughput without any difference in
functionnality. :-)


Gérard Roudier
Not CEO, not President of anything.

> Regards,
>
>
> Andre Hedrick
> CEO/President, LAD Storage Consulting Group
> Linux ATA Development
> Linux Disk Certification Project

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