From: Helge Hafting <helge.hafting@hist.no>
To: Timothy Miller <miller@techsource.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Block Device Caching
Date: Wed, 30 Jun 2004 10:29:40 +0200 [thread overview]
Message-ID: <40E279F4.4090708@hist.no> (raw)
In-Reply-To: <40E1FDEC.6020606@techsource.com>
Timothy Miller wrote:
>
>
> Markus Schaber wrote:
>
>> This lead us to the conclusion that block devices do not cache, but the
>> filesystem does. But subsequently, I ran some tests on my developer
>> machine (Pentium 4 Mobile Laptop).
>
>
>
> I had kernel experts repeatedly insist to me that block devices were
> cached, while all of my tests (using dd to or from, say, /dev/sda1 or
> whatever) indicated that there was absolutely no caching whatsoever.
Well, any cache is dropped when the device is closed. "dd" closes the device
when it finishes.
Try a program that reads the same two blocks (spaced videly apart)
over and over from the same open file descriptor. With _no_ caching
you'll see
the drive seeking all the time. With caching, you won't.
Helge Hafting
next prev parent reply other threads:[~2004-06-30 8:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-06-29 22:20 Block Device Caching Markus Schaber
2004-06-29 22:46 ` Andreas Dilger
2004-06-29 23:41 ` Timothy Miller
2004-06-30 6:30 ` Markus Schaber
2004-07-02 9:21 ` CCISS driver and Caching (was: Block Device Caching) Markus Schaber
2004-06-29 23:40 ` Block Device Caching Timothy Miller
2004-06-30 8:29 ` Helge Hafting [this message]
[not found] ` <20040630123828.7d48c6e6@kingfisher.intern.logi-track.com>
[not found] ` <40E543D7.9030303@hist.no>
2004-07-02 12:01 ` Markus Schaber
2004-07-02 12:56 ` FabF
2004-07-05 15:07 ` Markus Schaber
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