Re: Announce: zerotools (tools to keep virtual machine disks cleaner)

[Aleksandr Koltsoff <czr@iki.fi>]

Hello,
Amaya wrote:
> I maintain the package perforate. It contains a very similar utility,
> zum, that is just a small c binary that seems to do the same.

Thanks for the perforate info.

zum is a resparser for existing files. This is quite different from
filling existing files with binary zero. A resparsing done inside
virtual disks would not make things any easier when compressing the
virtual disk (from outside the vm).

Many people seem to misunderstand the exact problem which zerotools
tries to solve though :-).

> Also take a look at http://bugs.debian.org/294297 and be warned that
> these kind of utilities can ruin a vfat file system (just warning you
> in case you have not thought about it).

One could probably implement the resparsing operation that zum does
using a similar LD_PRELOAD technique, but as you note yourself, sparse
files have interesting properties when the underlying filesystem does
not support sparse files. Also creating new files from inside unlink()
for doing resparsing doesn't at all sound like a thing that I'd like to
see in my systems. zerounlink never creates new files, hence it doesn't
trip over full inode tables and such.

Summa summarum, I don't think that zerotools and perforate/zum overlap
at all. The closest parallel between zum and zerotools is in zerofile,
which is just a mindless utility. I don't imagine people will use
zerofile a lot since the LD_PRELOAD-mechanism (with the wrapper) is much
easier and automatic.

ak.