I just ran into an issue while trying to compact my Virtualbox hard drive images. On virtual NTFS filesystems I usually run defrag twice, then rely on a tool called sdelete (download page) to zero the free space within the image. Afterwards I use vboxmanage to reduce the image size.
This time either zeroing the free space or the shrinking process seemed to fail. The supposedly compressed images needed even more space than before. It took me a while to figure out what happened – the parameters of sdelete have changed:
C:\>sdelete
SDelete - Secure Delete v1.6
Copyright (C) 1999-2010 Mark Russinovich
Sysinternals - www.sysinternals.com
usage: sdelete [-p passes] [-s] [-q] <file or directory> ...
sdelete [-p passes] [-z|-c] [drive letter] ...
-a Remove Read-Only attribute
-c Clean free space
-p passes Specifies number of overwrite passes (default is 1)
-q Don't print errors (Quiet)
-s or -r Recurse subdirectories
-z Zero free space (good for virtual disk optimization)
It feels like 99% of the tips concerning zeroing the free space by calling sdelete -c (the old option for zeroing) seem to be outdated. Even worse: the “clean free space” feature shows the same output as “zero free space”.
So this should (currently) be a working procedure:
- Run the Windows “defrag” tool twice.
- (Download and) run “sdelete -z” to zero the free space.
- Use vboxmanage “modifyvdi IMAGE.vdi –compact” to reduce the image size.