Strange behaviour of UFS2+SU FS on FreeBSD 8-Stable: dreadful perofrmance for old data, excellent for new.

[Kirk McKusick]

> Date: Fri, 26 Aug 2011 23:27:58 +0400
> From: Lev Serebryakov <lev at freebsd.org>
> Organization: FreeBSD Project
> To: Kirk McKusick <mckusick at mckusick.com>
> Cc: fs at freebsd.org
> Subject: Re: Strange behaviour of UFS2+SU FS on FreeBSD 8-Stable: dreadful
> 	perofrmance for old data, excellent for new.
> 
> Hello, Kirk.
> 
> You wrote 26 August 2011, 22:33:43:
> 
> > If your old disk was full for a long time and had a lot of activity,
> > the most recently created files are likely to have poor layout.
> > Copying them should give them an improved layout now that much
> > more space is available. Best is to copy one, then remove the=20
> > original copy. Copy the next one and remove its old copy, etc.
> > Please let me know if this works, as if it does not, something
> > is wrong with growfs.
> 
> Ok, I'll write script for this monotonous work :) I could even copy
> them one-by-one via other file system )copy out, delete, copy in).
> Will it be better or not?
> 
> --
> // Black Lion AKA Lev Serebryakov <lev at FreeBSD.org>

Given how much bigger your new filesystem has grown, copying out to
another filesystem should not be necessary. However, it will likely 
be quicker to copy out to another filesystem as you will be using
two spindles instead of seeking back and forth on one. But before
doing all that work, try copying one file to ensure that you get the
expected speedup.

	Kirk McKusick