The  zeroer  utility can be used to flush the empty space on a disk. In contrary
to the dd utility, zeroer doesn't wipe  existing  files  on  a partition.  It
overwrites  the  unallocated disk space around existing files, which means that
deleted files cannot be restored anymore  after processing  a  certain
partition  with zeroer. The utility's principle consists in writing huge
zero-padded memory blocks to a file. To a cer- tain extent this works similar to
the dd program, however zeroer dynam- ically reduces the blockwriter's buffer
size when the disk is going  to be  full.  Thus,  smaller  fragments of
unallocated partition space are also flushed, even though the largest
unallocated  disk  areas  can  be written with huge blocks and this means more
speed.

zeroer's  principle  is  quite  simple  and there is no guarantee, that zeroer
works reliably on every file system, since zeroer  doesn't  know the  way  a
file system works exactly. However, most file systems use a mix of a centralized
disk block addressing  table  (e.g.  inodes,  file allocation  table) and
multiple peripheral directory/ file descriptors.  zeroer has been multi-pass
tested on UFS, FAT and NTFS and  the  test's results  showed, that zeroer
operates quite reliably on these file sys- tems.

Warning: The current version of zeroer doesn't remove file or directory meta
data  like  file and directory names, sizes, dates, modes. Only a file's content
is overwritten. Metadata scrambling will be  implemented in a future release.

WWW: http://critical.ch/zeroer/
