I have a number of Xen virtual machines running on a number of Linux servers. These VMs store their disk images in Linux LVM volumes with device names along the lines of /dev/xenVG/SERVER001OS and so on. I'd like to take regular backups of those disk images so I can restore the VMs in case we need to (the LVM devices are already mirrored with DRBD between two physical machines each, I'm just being extra paranoid here).
How do I go about this? Oviously the first step is to snapshot the LVM device, but how do I then transfer data to a backup server in the most efficient manner possible? I could simply copy the whole device, something along the lines of:
dd if=/dev/xenVG/SERVER001OS | ssh administrator@backupserver "dd of=/mnt/largeDisk/SERVER001OS.img"
…but that would take a lot of bandwidth. Is there an rsync-like tool for synching contents of whole disk blocks between remote servers? Something like:
rsync /dev/xenVG/SERVER001OS backupServer:/mnt/largeDisk/SERVER001OS.img
If I understand rsync's man page correctly, the above command won't actually work (will it?), but it shows what I'm aiming for. I understand the –devices rsync option is to copy devices themselves, not the contents of those devices. Making a local copy of the VM image before syncing it with the remote server isn't an option as there isn't the disk space.
Is there a handy utility that can synch between block devices and a backup file on a remote server? I can write one if I have to, but an existing solution would be better. Have I missed an rsync option that does this for me?
Best Answer
Standard rsync is missing this feature, but there is a patch for it in the rsync-patches tarball (copy-devices.diff) which can be downloaded from http://rsync.samba.org/ftp/rsync/ After appling and recompiling, you can rsync devices with the --copy-devices option.