ZFS clone script
ZFS has some magical features, comparable to NetApp’s WAFL capabilities. One of the less-used on is the ZFS send/receive, which can be utilised as an engine below something much like NetApp’s SnapMirror or SnapVault.
The idea, if you are not familiar with NetApp’s products, is to take a snapshot of a dataset on the source, and clone it to a remote storage. Then, take another snapshot, and clone only the delta between both snapshots, and so on. This allows for cloning block-level changes only, which reduces clone payload and the time required to clone it.
Copy and save this file as clone_zfs_snapshots.sh. Give it execution permissions.
#!/bin/bash
# This script will clone ZFS snapshots incrementally over SSH to a target server
# Snapshot name structure: filesystem@${TGT_HASH}_INT ; where INT is an increment number
# Written by Etzion. Feel free to use. See more stuff in my blog at https://run.tournament.org.il
# Arguments:
# $1: ZFS filesystem name
# $2: (target ZFS system):(target ZFS filesystem)
IAM=$0
ZFS=/sbin/zfs
LOCKDIR=/dev/shm
LOCAL_SNAPS_TO_LEAVE=3
RESUME_LIMIT=3
### FUNCTIONS ###
# Sanity and usage
function usage() {
echo "Usage: $IAM SRC REMOTE_SERVER:ZFS_TARGET (port=SSH_PORT)"
echo "ZFS_TARGET is the parent of filesystems which will be created with the original source names"
echo "Example: $IAM share/test backupsrv:backup"
echo "It will create a filesystem 'test' under the pool 'backup' on 'backupsrv' with clone"
echo "of the current share/test ZFS filesystem"
echo "This script is (on purpose) not a recursive script"
echo "For the script to work correctly, it *must* have SSH key exchanged from source to target"
exit 0
}
function abort() {
# exit errorously with a message
echo "$@"
pkill -P $$
remove_lock
exit 1
}
function parse_parameters() {
# Parses command line parameters
# called with $*
SRC_FS=$1
shift
TGT=$1
shift
for i in $*
do
case ${i} in
port=*) PORT=${i##*=}
;;
hash=*) HASH=${i##*=}
;;
esac
done
TGT_SYS=${TGT%%:*}
TGT_FS=${TGT##*:}
# Use a short substring of MD5sum of the target name for later unique identification
SRC_DIRNAME_FS=${SRC_FS#*/}
if [ -z "$hash" ]
then
TGT_FULLHASH="`echo $TGT_FS/${SRC_DIRNAME_FS} | md5sum -`"
TGT_HASH=${TGT_FULLHASH:1:7}
else
TGT_HASH=${hash}
fi
}
function sanity() {
# Verify we have all details
[ -z "$SRC_FS" ] && usage
[ -z "$TGT_FS" ] && usage
[ -z "$TGT_SYS" ] && usage
$ZFS list -H -o name $SRC_FS > /dev/null 2>&1 || abort "Source filesystem $SRC_FS does not exist"
# check_target_fs || abort "Target ZFS filesystem $TGT_FS on $TGT_SYS does not exist, or not imported"
}
function remove_lock() {
# Removes the lock file
\rm -f ${LOCKDIR}/$SRC_LOCK
}
function construct_ssh_cmd() {
# Constract the remote SSH command
# Here is a good place to put atomic parameters used for the SSH
[ -z "${PORT}" ] && PORT=22
SSH="ssh -p $PORT $TGT_SYS -o ConnectTimeout=3"
CONTROL_SSH="$SSH -f"
}
function get_last_remote_snapshots() {
# Gets the last snapshot name on a remote system, to match it to our snapshots
remoteSnapTmpObj=`$SSH "$ZFS list -H -t snapshot -r -o name ${TGT_FS}/${SRC_DIRNAME_FS}" | grep ${SRC_DIRNAME_FS}@ | grep ${TGT_HASH}`
# Create a list of all snapshot indexes. Empty means its the first one
remoteSnaps=""
for snapIter in ${remoteSnapTmpObj}
do
remoteSnaps="$remoteSnaps ${snapIter##*@${TGT_HASH}_}"
done
}
function check_if_remote_snapshot_exists() {
# Argument: $1 ->; Name of snapshot
# Checks if this snapshot exists on remote node
$SSH "$ZFS list -H -t snapshot -r -o name ${TGT_FS}/${SRC_DIRNAME_FS}@${TGT_HASH}_${newLocalIndex}"
return $?
}
function get_last_local_snapshots() {
# This function will return an array of local existing snapshots using the existing TGT_HASH
localSnapTmpObj=`$ZFS list -H -t snapshot -r -o name $SRC_FS | grep $SRC_FS@ | grep $TGT_HASH `
# Convert into a list and remove the HASH and everything before it. We should have clear list of indexes
localSnapList=""
for snapIter in ${localSnapTmpObj}
do
localSnapList="$localSnapList ${snapIter##*@${TGT_HASH}_}"
done
# Convert object to array
localSnapList=( $localSnapList )
# Get the last object
let localSnapArrayObj=${#localSnapList[@]}-1
}
function delete_snapshot() {
# This function will delete a snapshot
# arguments: $1 -> snapshot name
[ -z "$1" ] && abort "Cleanup snapshot got no arguments"
$ZFS destroy $1
#$ZFS destroy ${SRC_FS}@${TGT_HASH}_${newLocalIndex}
}
function find_matching_snapshot() {
# This function will attempt to find a matching snapshot as a replication baseline
# Gets the latest local snapshot index
localRecentIndex=${localSnapList[$localSnapArrayObj]}
# Gets the latest mutual snapshot index
while [ $localSnapArrayObj -ge 0 ]
do
# Check if the current counter already exists
if echo "$remoteSnaps" | grep -w ${localSnapList[$localSnapArrayObj]} > /dev/null 2>&1
then
# We know the mutual index.
commonIndex=${localSnapList[$localSnapArrayObj]}
return 0
fi
let localSnapArrayObj--
done
# If we've reached here - there is no mutual index!
abort "There is no mutual snapshot index, you will have to resync"
}
function cleanup_snapshots() {
# Creates a list of snapshots to delete and then calls delete_snapshot function
# We are using the most recent common index, $localSnapArrayObj as the latest reference for deletion
let deleteArrayObj=$localSnapArrayObj-${LOCAL_SNAPS_TO_LEAVE}
snapsToDelete=""
# Construct a list of snapshots to delete, and delete it in reverse order
while [ $deleteArrayObj -ge 0 ]
do
# Construct snapshot name
snapsToDelete="$snapsToDelete ${SRC_FS}@${TGT_HASH}_${localSnapList[$deleteArrayObj]}"
let deleteArrayObj--
done
snapsToDelete=( $snapsToDelete )
snapDelete=0
while [ $snapDelete -lt ${#snapsToDelete[@]} ]
do
# Delete snapshot
delete_snapshot ${snapsToDelete[$snapDelete]}
let snapDelete++
done
}
function initialize() {
# This is a unique case where we initialize the first sync
# We will call this procedure when $remoteSnaps is empty (meaning that there was no snapshot whatsoever)
# We have to verify that the target has no existing old snapshots here
# is it empty?
echo "Going to perform an initialization replication. It might wipe the target $TGT_FS completely"
echo "Press Enter to proceed, or Ctrl+C to abort"
read "abc"
### Decided to remove this check
### [ -n "$LOCSNAP_LIST" ] && abort "No target snapshots while local history snapshots exists. Clean up history and try again"
RECEIVE_FLAGS="-sFdvu"
newLocalIndex=1
# NEW_LOC_INDEX=1
create_local_snapshot $newLocalIndex
open_remote_socket
sleep 1
$ZFS send -ce ${SRC_FS}@${TGT_HASH}_${newLocalIndex} | nc $TGT_SYS $NC_PORT 2>&1
if [ "$?" -ne "0" ]
then
# Do no cleanup current snapshot
# delete_snapshot ${SRC_FS}@${TGT_HASH}_${newLocalIndex}
abort "Failed to send initial snapshot to target system"
fi
sleep 1
# Set target to RO
$SSH $ZFS set readonly=on $TGT_FS
[ "$?" -ne "0" ] && abort "Failed to set remote filesystem $TGT_FS to read-only" # No need to remove local snapshot
}
function create_local_snapshot() {
# Creates snapshot on local storage
# uses argument $1
[ -z "$1" ] && abort "Failed to get new snapshot index"
$ZFS snapshot ${SRC_FS}@${TGT_HASH}_${1}
[ "$?" -ne "0" ] && abort "Failed to create local snapshot. Check error message"
}
function open_remote_socket() {
# Starts remote socket via SSH (as the control operation)
# port is 3000 + three-digit random number
let NC_PORT=3000+$RANDOM%1000
$CONTROL_SSH "nc -l -i 90 $NC_PORT | $ZFS receive ${RECEIVE_FLAGS} $TGT_FS > /tmp/output 2>&1 ; sync"
#$CONTROL_SSH "socat tcp4-listen:${NC_PORT} - | $ZFS receive ${RECEIVE_FLAGS} $TGT_FS > /tmp/output 2>&1 ; sync"
#zfs send -R zp03@01 | zfs receive -Fdvu zpnew
}
function send_zfs() {
# Do the heavy lifting of opening remote socket and starting ZFS send/receive
open_remote_socket
sleep 1
$ZFS send -ce -I ${SRC_FS}@${TGT_HASH}_${commonIndex} ${SRC_FS}@${TGT_HASH}_${newLocalIndex} | nc -i 90 $TGT_SYS $NC_PORT
#$ZFS send -ce -I ${SRC_FS}@${TGT_HASH}_${commonIndex} ${SRC_FS}@${TGT_HASH}_${newLocalIndex} | socat tcp4-connect:${TGT_SYS}:${NC_PORT} -
sleep 20
}
function increment() {
# Create a new snapshot with the index $localRecentIndex+1, and replicate it to the remote system
# Baseline is the most recent common snapshot index $commonIndex
RECEIVE_FLAGS="-Fsdvu" # With an 'F' flag maybe?
# Handle the case of latest snapshot in DR is newer than current latest snapshot, due to mistaken deletion
remoteSnaps=( $remoteSnaps )
let remoteIndex=${#remoteSnaps[@]} # Get last snapshot on DR
if [ ${localRecentIndex} -lt ${remoteIndex} ]
then
let newLocalIndex=${remoteIndex}+1
else
let newLocalIndex=localRecentIndex+1
fi
create_local_snapshot $newLocalIndex
send_zfs
# if [ "$?" -ne "0" ]
# then
# Cleanup current snapshot
#delete_snapshot ${SRC_FS}@${TGT_HASH}_${newLocalIndex}
#abort "Failed to send incremental snapshot to target system"
# fi
if ! verify_correctness
then
if ! loop_resume # If we can
then
# We either could not resume operation or failed to run with the required amount of iterations
# For now we abort.
echo "Deleting local snapshot"
delete_snapshot ${SRC_FS}@${TGT_HASH}_${newLocalIndex}
abort "Remote snapshot should have the index of the latest snapshot, but it is not. The current remote snapshot index is ${commonIndex}"
fi
fi
}
function loop_resume() {
# Attempts to loop over resuming until limit attempt has been reached
REMOTE_TOKEN=$($SSH "$ZFS get -Ho value receive_resume_token ${TGT_FS}/${SRC_DIRNAME_FS}")
if [ "$REMOTE_TOKEN" == "-" ]
then
return 1
fi
# We have a valid resume token. We will retry
COUNT=1
while [ "$COUNT" -le "$RESUME_LIMIT" ]
do
# For ease of handline - for each iteration, we will request the token again
echo "Attempting resume operation"
REMOTE_TOKEN=$($SSH "$ZFS get -Ho value receive_resume_token ${TGT_FS}/${SRC_DIRNAME_FS}")
let COUNT++
open_remote_socket
$ZFS send -e -t $REMOTE_TOKEN | nc -i 90 $TGT_SYS $NC_PORT
#$ZFS send -e -t $REMOTE_TOKEN | socat tcp4-connect:${TGT_SYS}:${NC_PORT} -
sleep 20
if verify_correctness
then
echo "Done"
return 0
fi
done
# If we've reached here, we have failed to run the required iterations. Lets just verify again
return 1
}
function verify_correctness() {
# Check remote index, and verify it is correct with the current, latest snapshot
if check_if_remote_snapshot_exists
then
echo "Replication Successful"
return 0
else
echo "Replication failed"
return 1
fi
}
### MAIN ###
[ `whoami` != "root" ] && abort "This script has to be called by the root user"
[ -z "$1" ] && usage
parse_parameters $*
SRC_LOCK=`echo $SRC_FS | tr / _`
if [ -f ${LOCKDIR}/$SRC_LOCK ]
then
echo "Already locked. If should not be the case - remove ${LOCKDIR}/$SRC_LOCK"
exit 1
fi
sanity
touch ${LOCKDIR}/$SRC_LOCK
construct_ssh_cmd
get_last_remote_snapshots # Have a string list of remoteSnaps
# If we dont have remote snapshot it should be initialization
if [ -z "$remoteSnaps" ]
then
initialize
echo "completed initialization. Done"
remove_lock
exit 0
fi
# We can get here only if it is not initialization
get_last_local_snapshots # Have a list (array) of localSnaps
find_matching_snapshot # Get the latest local index and the latest common index available
increment # Creates a new snapshot and sends/receives it
cleanup_snapshots # Cleans up old local snapshots
pkill -P $$
remove_lock
echo "Done"
A manual initial run should be called manually. If you expect a very long initial sync, you should run it in tmux to screen, to avoid failing in the middle.
To run the command, run it like this:
./clone_zfs_snapshots.sh share/my-data backuphost:share
This will create under the pool ‘share’ in the host ‘backuphost’ a filesystem matching the source (in this case: share/my-data) and set it to read-only. The script will create a snapshot with a unique name based on a shortened hash of the destination, with a counting number suffix, and start cloning the snapshot to the remote host. When called again, it will create a snapshot with the same name, but different index, and clone the delta to the remote host. In case of a disconnection, the clone will retry a few times before failing.
Note that the receiving side does not remove snapshots, so handling (too) old snapshots on the backup host remains up to you.
Hi!
Interesting, have you tried https://github.com/psy0rz/zfs_autobackup ?
I build (vibe coding) a wrapper around for better output/logging
https://github.com/Mstaaravin/crontab_zfs-autobackup
Regards