Just create a new volume with the remaining space you have on the lvm (that of course you left over for this exact reason!). It does not need to be a big enough volume to be the size of the one to be backed up, just enough to track changes while you copy the files!
lvcreate -L500G -s -n vmbackup /dev/vg0/lv0 (or whatever your pool of disk is called) mount /dev/vg0/vmbackup /mnt/backups/ cd /mnt/backups/ copy copy copy (probably cp --sparse=always) lvremove /dev/vg0/vmbackup If this fails because it says it is in use (but fuser and lsof prove otherwise): udevadm control --stop-exec-queue -- udev could be in the way -- Retry the lvremove. udevadm control --start-exec-queue -- might want to add a tweaked blacklist rule: -- /lib/udev/rules.d/80-udisks.rules: comment out the line with the watch rule: #KERNEL=="dm-*", OPTIONS+="watch"
More info here:
http://www.sysresccd.org/Sysresccd-manual-en_LVM_Making-consistent-backups-with-LVM