On Sat, May 8, 2010 at 5:04 AM, Lutz Schumann <presa...@storageconcepts.de> wrote: > Now If I think there would be "write all zero, clear the block again" in ZFS > (which I suggest in this thread) I could do the following: > > Fill the disks within the VM's with all zero (dd if=/dev/zero of=/MYFILE > bs=1M ...). This could effectibly write a lot for all-zero blocks to the > comstar and zfs. ZFS could then free the blocks and I could then send the > zvol to backup. This could mean 10 GB used in VM -> zvol size of ~10 GB -> 10 > GB transfered.
If you set compression=zle, you'll only be compressing strings of 0s. It's low overhead for the zfs system to maintain. Doing a dd like you suggest works well to reclaim most freed space from the zvol. You can unlink the file that you're writing to before the dd is finished so that the VM doesn't see the disk as full for more than a split second. Windows VMs can use SDelete (http://technet.microsoft.com/en-us/sysinternals/bb897443.aspx) to zero-fill their disks to free space on the server. -B -- Brandon High : bh...@freaks.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
