From: Alexei_Roudnev (Alexei_Roudnev_at_exigengroup.com)
Date: Tue Aug 28 2007 - 19:59:10 CEST
Message-ID: <008201c7e99d$22e356d0$6401a8c0@alexh> From: "Alexei_Roudnev" <Alexei_Roudnev@exigengroup.com> Date: Tue, 28 Aug 2007 10:59:10 -0700 Subject: Re: [suse-sles-e] Slow direct I/O performance SLES 10 SP1
DirectIO speed can be low for the tape - what did you expected? Buffered IO
is faster in many cases. I don't understand why you counted it as a bug.
Oracle uses DirectIO to eliminate double buffering and to ensure that writes
are passed thru. Not so much for performance.
More likely, DirectIO was not broken in your case, but DirectIO parameters
in application was not well tuned.
----- Original Message -----
From: "Bernd Melchers" <melchers@CIS.FU-Berlin.DE>
To: "Alexei_Roudnev" <Alexei_Roudnev@exigengroup.com>
Cc: <suse-sles-e@suse.com>; "Andreas Mock" <Andreas.Mock@web.de>
Sent: Tuesday, August 28, 2007 1:23 AM
Subject: Re: [suse-sles-e] Slow direct I/O performance SLES 10 SP1
> I use directIO with SLES9 SP3 (and oracle) all the time, without any
> problems. Why do you think that it's broken?
I was directed by my vendor (SGI) to use directIO for streaming backup data
from raid to all of my four Ultrium2-Tape Drives. This was supposed to be
more CPU efficient than bufferedIO.
But the transfer rates were too slow with directIO (7-22 MB/sec per drive).
Then it was said, directIO is broken in SLES9 and i should switch back to
bufferedIO, at least until SLES10. With bufferedIO the transfer rates
increases to 30-90 MB/sec per Ultrium2-drive, depending on compressability
of data.
HBA Cards are qlogic12160 and LSI53C1030 (LVD160, no Fiberchannel), cpus are
itanium2.
I don't see any reason for these bad directIO transfer rates.
mit freundlichen Grüßen
Bernd Melchers
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