Re: [Xen-users] Clean deleted space in linux diks?

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

Niels Dettenbach (Syndicat IT&Internet) wrote:

>  >We run different version of SLES. Are there any similar tools for linux
> > or a way of doing this in linux so the deleted space can be reclaimed?
> Shure, use dd or similiar tools.
>
> If you just want to overwrite with zeros you may do a:
>
> dd if=/dev/zero of=/dev/yourdiskorpartition
>
> (you may speed up write by giving a larger blocksize option like 
> i.e. bs=1024k )
> if you have enough random data / fast data souce you may use that 
> instead of /dev/zero .
In this case he is wanting zeros so that the SAN will make the storage sparse.

If the disk is large, it may be a bit of a problem making a single 
large file. The OP hasn't said which specific OS (32 vs 64 bit), or 
filesystem, so I don't know what the max file size is (I vaguely 
recall a 4G limit under some OS/filesystem combinations). He may have 
to do something like :
a=0 ; while [ $a -lt X ]
do
  dd if=/dev/zero of=null-file-$a bs=1024k count=1024
done
rm null-file*

replacing X with a value appropriate to the free space available. 
This will create 1GB files of zeros, so if there is 75G of free 
space, I'd set X to 76 just to be sure. Probably best to stop all 
unnecessary services so things don't barf when the disk is full.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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