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

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

James Pifer wrote:
>  > Either you are doing a block level volume copy (in which case you'll
> >  need to erase free space only), or you are doing a file copy in which
> >  case you'll start with an empty virtual volume which will expand in
> >  storage requirements as you copy files.
> Simon,
>
> Just to recap, I am trying to erase the free space only. I assume the
> new SAN is doing a block level copy, which is why it consumes the whole
> space. Once I erase the free space there is a reclamation process on the
> SAN that will make the disk thin/sparse.
>
> Yes, if I take a newly created thin disk, and do a file level restore or
> copy, the disk remains thin.
>
> For this example I have a disk called xvda. It has two partitions:
> xvda1 (swap)
> xvda2 (system)
>
> I would like to erase the free space on xvda2, which is running on
> sles11 with ext3.
>
> Several things were mentioned. If you don't mind repeating, what do you
> feel is the final solution?
My apologies, I mixed up who said what. Niels gave you information on 
erasing an entire partition (ie nuke the entire filesystem as well), 
I gave you information on  erasing free space only.
If I were doing it, I'd do one of these :

If there's a lot of free space and making huge files may be an issue

a=0 ; while [ $a -lt X ]
do
  dd if=/dev/zero of=null-file-$a bs=1024k count=1024
done
rm null-file*
X needs to be > amount of free space in GBytes.

If there isn't a huge amount of free space and/or making one big file 
isn't an issue.
dd if=/dev/zero of=null-file bs=1024k ; rm null-file
or
cat /dev/zero > null-file ; rm null-file

Both of these will write nulls into file(s) until the filesystem is 
full, then delete them. Depending on the space involved, they may 
take some time, and to avoid problems if anything tries to write a 
file while the disk is full you should stop as many processes as 
possible.
--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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