From: Robert Hancock <hancockr@shaw.ca>
To: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: io performance...
Date: Wed, 18 Jan 2006 19:58:59 -0600 [thread overview]
Message-ID: <43CEF263.9060102@shaw.ca> (raw)
In-Reply-To: <5wdKh-5wF-15@gated-at.bofh.it>
Jeff V. Merkey wrote:
> Max Waterman wrote:
>
>> One further question. I get these messages 'in' dmesg :
>>
>> sda: asking for cache data failed
>> sda: assuming drive cache: write through
>>
>> How can I force it to be 'write back'?
>
> Forcing write back is a very bad idea unless you have a battery backed
> up RAID controller.
This is not what these messages are referring to. Those write through
vs. write back messages are referring to detecting the drive write cache
mode, not setting it. Whether or not the write cache is enabled is used
to determine whether the sd driver uses SYNCHRONIZE CACHE commands to
flush the write cache on the device. If the drive says its write cache
is off or doesn't support determining the cache status, the kernel will
not issue SYNCHRONIZE CACHE commands. This may be a bad thing if the
device is really using write caching..
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/
next parent reply other threads:[~2006-01-19 1:57 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <5vx8f-1Al-21@gated-at.bofh.it>
[not found] ` <5wbRY-3cF-3@gated-at.bofh.it>
[not found] ` <5wdKh-5wF-15@gated-at.bofh.it>
2006-01-19 1:58 ` Robert Hancock [this message]
2006-01-19 13:14 ` io performance Max Waterman
2006-01-19 14:08 ` Alan Cox
2006-01-20 4:09 ` Max Waterman
2006-01-20 4:27 ` Alexander Samad
2006-01-20 12:52 ` Alan Cox
2006-01-19 11:39 Al Boldi
-- strict thread matches above, loose matches on Subject: below --
2006-01-16 7:35 Max Waterman
2006-01-16 7:32 ` Jeff V. Merkey
2006-01-17 13:57 ` Jens Axboe
2006-01-17 19:17 ` Jeff V. Merkey
2006-01-16 8:35 ` Pekka Enberg
2006-01-17 17:06 ` Phillip Susi
2006-01-18 7:24 ` Max Waterman
2006-01-18 15:19 ` Phillip Susi
2006-01-20 5:58 ` Max Waterman
2006-01-20 13:42 ` Ian Soboroff
2006-01-25 6:36 ` Max Waterman
2006-01-25 14:19 ` Ian Soboroff
2006-01-25 13:09 ` Bernd Eckenfels
2006-01-18 3:02 ` Max Waterman
2006-01-18 4:30 ` Jeff V. Merkey
2006-01-18 5:09 ` Max Waterman
2006-01-18 4:37 ` Jeff V. Merkey
2006-01-18 7:06 ` Max Waterman
2006-01-18 9:21 ` Alan Cox
2006-01-18 15:48 ` Phillip Susi
2006-01-18 16:25 ` Bartlomiej Zolnierkiewicz
2006-01-19 0:48 ` Adrian Bunk
2006-01-19 13:18 ` Max Waterman
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