Filesystem space accounting bug

Filesystem space accounting bug

[Walter Hofmann]

Hi,

I have a backup script which creates a filesystem image which is later 
written to DVD. It is created & loop-mounted with

 dd if=/dev/zero of=${DARIMAGE} bs=1024k count=4460 || exit 1
 mke2fs -F -b 4096 -m 0 -N 32 -O sparse_super -L BACKUP ${DARIMAGE} || exit 1
 sync
 mount /mnt/dar
 touch /mnt/dar/backup-stamp

Then I use the "dar" utility to create a single large file on this. I
believe, but have not checked, that dar writes the file linearly. dar is
instructed to stop writing to the filesystem before it reaches 4GB. 

However, recently, dar failed after approx. 3GB with ENOSPC. The 
filesystem was still mounted, so I could check that there really were 
only 3GB written to it. Still, I could not even create a 1 byte file on 
it, although there should be around 1GB free space left.

There were no error messages logged. I unmounted the image and ran 
e2fsck on it and it reported that the free block count in a number of 
groups on the filesystem was wrong. 

I'm using Linux 2.6.6. I tried to reproduce this, but now it works
again.

Walter

Re: Filesystem space accounting bug

[Calvin Spealman]

I had a similar problem a few days ago. My wife was working in GIMP and
called me in, complaining about an Out Of Space error. I didn't find it out
of the ordinary, so I removed lots of temp files and tarballs of things
already installed. I cleared up a few gigs.

A few hours later, she got the same errors. I deleted all the videos I
already had backed-up on CD, since my DVD player can play those anyway.

A few hours later, she got the same errors. I knew at this point something
weird was going on. A few friends suggested my system had been compromised,
but I knew better. Eventually I tried rebooting to a Live CD, so I could
run fsck.ext3, but everything now looked fine. I haven't had the problem
since, and I have no idea what caused it.

Walter Hofmann wrote:

> Hi,
> 
> I have a backup script which creates a filesystem image which is later
> written to DVD. It is created & loop-mounted with
> 
>  dd if=/dev/zero of=${DARIMAGE} bs=1024k count=4460 || exit 1
>  mke2fs -F -b 4096 -m 0 -N 32 -O sparse_super -L BACKUP ${DARIMAGE} ||
>  exit 1 sync
>  mount /mnt/dar
>  touch /mnt/dar/backup-stamp
> 
> Then I use the "dar" utility to create a single large file on this. I
> believe, but have not checked, that dar writes the file linearly. dar is
> instructed to stop writing to the filesystem before it reaches 4GB.
> 
> However, recently, dar failed after approx. 3GB with ENOSPC. The
> filesystem was still mounted, so I could check that there really were
> only 3GB written to it. Still, I could not even create a 1 byte file on
> it, although there should be around 1GB free space left.
> 
> There were no error messages logged. I unmounted the image and ran
> e2fsck on it and it reported that the free block count in a number of
> groups on the filesystem was wrong.
> 
> I'm using Linux 2.6.6. I tried to reproduce this, but now it works
> again.
> 
> Walter

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