Re: Making discard/fstrim reliable

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Apr 03, 2014 at 07:08:34PM +0200, Lukáš Czerner wrote:
> All that said, while discard is a interesting functionality and can
> be abused in many _many_ ways. It looks like what you really need is
> something that is currently available in fallocate(1) from
> util-linux package. The option to look for is --dig-holes:
> 
> -d, --dig-holes
>       Detect  and  dig holes. Makes the file sparse in-place, without using extra disk space.
>       The minimal size of the hole depends on filesystem I/O block size (usually 4096 bytes).
>       Also, when using this option, --keep-size is implied.
> 
>       You can think of this as doing a "cp --sparse" and renaming the dest file as the origi‐
>       nal, without the need for extra disk space.

This applies to single host files right?

virt-sparsify takes a disk image and sparsifies it, by examining the
internals of the disk image to find unused space (not *zero* space,
but space that's unused -- it could contain deleted files or other
garbage).

Rich.

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