linux-ext4 - Re: [Jfs-discussion] benchmark results

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Message-ID: <4B36333B.3030600@hp.com>
Date:	Sat, 26 Dec 2009 11:00:59 -0500
From:	jim owens <jowens@...com>
To:	Christian Kujau <lists@...dbynature.de>
CC:	Larry McVoy <lm@...mover.com>, tytso@....edu,
	jfs-discussion@...ts.sourceforge.net, linux-nilfs@...r.kernel.org,
	xfs@....sgi.com, reiserfs-devel@...r.kernel.org,
	Peter Grandi <pg_jf2@....for.sabi.co.UK>,
	ext-users <ext3-users@...hat.com>, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org
Subject: Re: [Jfs-discussion] benchmark results

Christian Kujau wrote:

> I was using "sync" to make sure that the data "should" be on the disks 

Good, but not good enough for many tests... info sync

CONFORMING TO
       POSIX.2

NOTES
       On Linux, sync is only guaranteed to  schedule  the  dirty  blocks  for
       writing;  it  can  actually take a short time before all the blocks are
       finally written.

This is consistent with all the feels-like-unix OSes I have used.

And to make it even more random, the hardware (drive/controller)
write cache state needs to be accounted for, and what the filesystem
does if anything to try to ensure device-cache-to-media consistency.

That does not mean I'm saying the tests are invalid or not useful,
only that people need to evaluate "what do they really tell me".

jim
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