ADSM-L

Re: [ADSM-L] ITDT write speed tests vs. dd write speed tests

2010-04-28 07:59:16
Subject: Re: [ADSM-L] ITDT write speed tests vs. dd write speed tests
From: Michael Green <mishagreen AT GMAIL DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Wed, 28 Apr 2010 14:57:29 +0300
Folks, I'd truly appreciate if somebody with a moment to spare and
appropriate equipment at hand would run a couple of tests as shown
below and report back to the list.
--
Warm regards,
Michael Green



On Sat, Apr 10, 2010 at 1:47 AM, Michael Green <mishagreen AT gmail DOT com> 
wrote:
> I've been playing with ITDT v4 for quite some time now. I installed it
> on one of my production servers which is a hefty
> IBM x3850, SLES10 SP2 x64, lin_tape 1.34. The drives are LTO4.
> The FC fabric is 4Gb all along from the server to the library.
>
> I'm getting mixed results that I cannot explain.
> Using the "Full write" test from ITDT using Incompressible data and
> 256K transfer rate I consistently score above 100MB/sec write rates.
> At the same time using simple dd method (with compression turned off,
> same drive, same cartridge) as described in Richards ADSM Quick facts
> (search for THROUGHPUT MEASUREMENT topic) I score no more than
> 45MB/sec.
> The dd method is simple:
> 1. turn drive compression off (using ITDT or tapeutil)
> 2. run
> # time dd if=/dev/zero of=/dev/IBMtape7 bs=256k count=40960.
> (40960 by 256K is 10240MB). Now measure the time and divide 10240MB by
> it. This test consistently yields ~45MB/sec in my experiments.
>
> TAR'ing similar amount of data in a few big files yields about
> 40MB/sec. The underlying disks (a mirror of 2 146GB SAS 3Gb drives)
> are well capable of providing 80MB/sec sustained.
>
> Anyone tried doing similar tests? Anyone bothered playing with ITDT
> read/write tests at all?
> --
> Warm regards,
> Michael Green
>

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