This may be useful in places where block devices can be unmounted from one machine and remounted on another, say to recover from hardware failure on the first machine. (I plan to use it on Amazon AWS' EBS volumes)
The key is to use the -'-zero n' option when reassembling Physical Volumes in lvcreate, and to use the same --size option as the done for the previous LVM setup.
A Volume Group stores its metadata in the Physical Volumes, and hence if you manage to reassemble all Physical Volumes of a Volume Group, you get the original Volume Group back. (Per responses of 'comps' on Freenode's #lvm channel, and confirmed by the testing below)
Now it is up to the Logical Volume creator to carve out volumes of the same size and from the same locations of this Volume Group.
# Legend: # LVM = Logical Volume Manager 2 # PV = Physical Volume # VG = Volume Group # LV = Logical Volume # FS = FileSystem # Make a temp directory to play in mkdir ~/lvm_test cd ~/lvm_test MINOR_NUMBER_START=100 MAX_DEVICES=8 for (( i = $MINOR_NUMBER_START ; i < $MINOR_NUMBER_START+$MAX_DEVICES ; ++i )); do # Make a few empty files dd if=/dev/zero of=dev$i bs=1024 count=20480 # Make a few loop devices sudo mknod -m660 lo$i b 7 $i sudo losetup lo$i dev$i # Create LVM PVs using these loop devices sudo pvcreate lo$i done # Create a VG over all the PVs, and name it vg1 sudo vgcreate vg1 lo* # Create a LV from the VG, and name it lv1 sudo lvcreate --name lv1 vg1 --size 100M # Make EXT3 FS on LV with name lv1 sudo mkfs.ext3 `sudo lvdisplay -c vg1/lv1 | cut -d : -f 1` # Make a directory to act as a mount point mkdir dir # Mount the LV on the directory sudo mount `sudo lvdisplay -c vg1/lv1 | cut -d : -f 1` dir # Create a 20 MB file filled with random data on this new FS sudo dd if=/dev/urandom of=dir/dd.out bs=1024 count=20480 # Make a backup of the file cp dir/dd.out ./dd.out # Now we perform the test where we remove all the LVs and PVs from the VG and # the VG itself, and then use the PVs to create a new VG and LV that can be # mounted with the filesystem intact. # Teardown the FS, LV and VG, but DONT remove the PVs sudo umount dir sudo lvchange --available n vg1/lv1 sudo lvremove vg1/lv1 sudo vgremove vg1 # Create a new VG using existing PVs, and name it vg_new sudo vgcreate vg_new lo* # Create a new LV on this VG, but DONT zero the first 1kB block; In essence, # retain the data on Physical Volumes. # Make sure to use the same size as previous LV (lv1), else mounting of EXT3 FS # won't work. sudo lvcreate --zero n --name lv_new vg_new --size 100M # Mount the LV on the directory; Note that we did not format.mkfs on the LV. sudo mount `sudo lvdisplay -c vg_new/lv_new | cut -d : -f 1` dir # Compare the backed-up copy of del.dd with the one just mounted from the new # Logical Volume sudo diff del.dd dir/del.dd # # Teardown sudo umount dir sudo lvchange --available n vg_new/lv_new sudo lvremove vg_new/lv_new sudo vgremove vg_new for (( i = $MINOR_NUMBER_START ; i < $MINOR_NUMBER_START+$MAX_DEVICES ; ++i )); do sudo pvremove lo$i sudo losetup -d lo$i done rm -rf ~/lvm_test unset MINOR_NUMBER_START unset MAX_DEVICES