Re: ext3 zerofree option and RedHat back port?

[Andreas Dilger <adilger sun com>]

On Sep 23, 2008  22:30 -0500, Eric Sandeen wrote:
> Ulf Zimmermann wrote:
> Ok, so you really want to zero the unused blocks in-place, and e2image
> writing out a new sparsified image isn't a ton of help.
> 
> The tool does that, I guess - but only on an unmounted or RO-mounted
> filesystem, right?  (plus I'd triple-check that it's doing things
> correctly, opening a block device and splatting zeros around, one hopes
> that it is!)

That is WAY to scary for me on a mounted filesystem.  It is racy if the
blocks become allocated.

Instead, what I always do when creating a sparse image for e2fsck test
cases is just "dd if=/dev/zero of=/mnt/fs/zeroes bs=64k; rm /mnt/fs/zeroes"
until the filesystem is full, then the file is deleted.  This will
leave blocks "empty" for the free space in the filesystem without
any special tools.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.