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LVMSnapSend

Currently in a very raw state, batteries NOT included.

You must never write directly to the destination LV.

Basic Usage

Assuming that

Example Testing

This is an example setting up 2 VGs and LVs on the same server for easier testing.

Set up thin LVM - SOURCE

apt install -y thin-provisioning-tools
apt install -y python
wget https://raw.githubusercontent.com/theraser/blocksync/master/blocksync.py

LV=thin_volume
VG=volg
THINPOOL=${VG}-thinpool
THINSIZE=7G   # Slightly smaller than the actual device.  Allow for resizing.
LVSIZE=3G
DEVICE=xvdf

pvcreate /dev/${DEVICE}
vgcreate ${VG} /dev/${DEVICE}

lvcreate -L ${THINSIZE} --thinpool ${THINPOOL}  ${VG} 

# Review the volume and metadata
lvdisplay ${VG}/${THINPOOL}

lvcreate -V ${LVSIZE} --thin -n ${LV} ${VG}/${THINPOOL}

Set up thin LVM - REPLICA

LV=thinv_replica
VG=vgreplica
THINPOOL=${VG}-thinpoolreplica
THINSIZE=7G   # Slightly smaller than the actual device.  Allow for resizing.
LVSIZE=3G
DEVICE=xvdg

pvcreate /dev/${DEVICE}
vgcreate ${VG} /dev/${DEVICE}

lvcreate -L ${THINSIZE} --thinpool ${THINPOOL}  ${VG} 

# Review the volume and metadata
lvdisplay ${VG}/${THINPOOL}

lvcreate -V ${LVSIZE} --thin -n ${LV} ${VG}/${THINPOOL}

Set up a file system and write to it

mkfs.ext4 /dev/${VG}/${LV}
mkdir /mnt/${VG}-${LV}
mount /dev/${VG}/${LV} /mnt/${VG}-${LV}/
rsync -av /etc /mnt/${VG}-${LV}/

Run the initial synchronisation

time java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapSend --vg volg --lv thin_volume --targetPath /dev/vgreplica/thinv_replica | ssh -C root@localhost "java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapReceive"

# There will be an error, because the initial sync must be done manually
lvcreate -s -n thin_volume_thinsendrcv_20190623_0554 volg/thin_volume
lvchange -ay -Ky /dev/volg/thin_volume_thinsendrcv_20190623_0554
python blocksync.py -c aes128-ctr /dev/volg/thin_volume_thinsendrcv_20190623_0554 root@localhost /dev/vgreplica/thinv_replica

# Check that the snapshots are created
lvs
md5sum /dev/volg/thin_volume_thinsendrcv_* /dev/vgreplica/thinv_replica

Regular Syncronisation

rsync -av /usr/bin /mnt/${VG}-${LV}/usr/
time java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapSend --vg volg --lv thin_volume --targetPath /dev/vgreplica/thinv_replica | ssh -C root@localhost "java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapReceive"

rsync -av /var /mnt/${VG}-${LV}/
time java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapSend --vg volg --lv thin_volume --targetPath /dev/vgreplica/thinv_replica | ssh -C root@localhost "java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapReceive"

rsync -av /usr/lib /mnt/volg-thin_volume/usr/
time java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapSend --vg volg --lv thin_volume --targetPath /dev/vgreplica/thinv_replica | ssh -C root@localhost "java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapReceive"

# Verify that it all worked
lvchange -ay -Ky /dev/volg/thin_volume_thinsendrcv_20190623_0610
md5sum /dev/volg/thin_volume_thinsendrcv_* /dev/vgreplica/thinv_replica

Debugging Problems

Test thin lvm is working properly

dmsetup message /dev/mapper/volg-volg--thinpool-tpool 0 reserve_metadata_snap
thin_delta  -m --snap1 $(lvs --noheadings -o thin_id volg/thin_volume_snap1) --snap2 $(lvs --noheadings -o thin_id volg/thin_volume_snap2) /dev/mapper/volg-volg--thinpool_tmeta
dmsetup message /dev/mapper/volg-volg--thinpool-tpool 0 release_metadata_snap

Run it in 2 parts

java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVMSnapSend --vg volg --s1 thin_volume_snap1 --s2 thin_volume_snap2 > /tmp/diff.ddxml

# Currently split into 2 parts and I had to hardcode the block size at the destination
cat /tmp/diff.ddxml | java -cp lvm-thin-sendrcv/lvm-thin-sendrcv.jar oneit.lvmsendrcv.LVSnapReceive