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[Xen-users] Will this work? (Zeroing free space)

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Aleix Dorca <adorca@xxxxxx>
  • Date: Fri, 21 Aug 2009 09:31:11 +0200
  • Delivery-date: Fri, 21 Aug 2009 00:32:58 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Hi guys,

I know this is not completely related to Xen but it affects my Xen setup.

I have some Win2003 VMs using disks via iscsi. I do backups using snapshots on LVM, dd and gzip. So far so good.

The thing is that the size of backups increases in time due to VM use although the used space in the VM disk does not increase. I'd like to zero the free space on the ext3 and ntfs partitions so gzip can compress more the files and the backups end up being somewhat smaller.

I wonder if this would work. I'd stop the VM and mount the disk temporarily on a iscsi client (maybe not necessary on ext3 partitions) and then I'd do a "dd if=/dev/zero of=file". After filling all available space on the disk I'd delete the file, thus leaving all free space zeroed.

Has any of you tried something similar?

Thanks a lot,


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