## Posts Tagged ‘data replication’

### ZFS clone script

Sunday, March 28th, 2021

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: [email protected]${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 "[email protected]"
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 [email protected] | 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 [email protected] | 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.

### Moving Exchange Data

Thursday, April 6th, 2006

Lets assume you have a method of point-in-time copy of Microsoft Exchange DB and logs, while the system is running, to an alternate server. Let’s assume, if we’re at that, that this point-in-time is consistent, and that you can mount this store (depending on using the similar directory structure, etc.), on an alternate server, and that it works correctly, aka, mounts without a problem. Scenario can be like this:

Server A: Microsoft Exchange, Storage group containing few mailbox stores, each on a different drive letter (E:, F:, G:, in our example), and the Storage Group’s logs are on a seperated drive, L:.

On Server B, we create a similar setup – Few mailbox stores, similar names, on E:, F:, G:, and we create (or move) the logs to reside on L:. We make sure this server’s patch level (or updates and versions) are similar to Server A.

We dismount the whole storage group, mark it to be overwritten by a restore, and replace the currently existing stores with our point-in-time from Server A. Great. Mounting the store, and, on a wider point of view, mounting the whole storage group’s components would be easy and painless. Our point-in-time is consistant, so it’s just like bringing up a storage group after unexpected shutdown.

Lets assume we were able to do so, we’re not finished yet. Each user’s attributes contain information pointing to the location of his/her mailbox, including the name of the store, and the name of the server. We need to change an AD attributes, per-user, for this point-in-time replication/DRP to work.

A friend of mine, Guy, has created such a script, just to solve this specific issue. It has some minor issues yet, but if you are aware of them, you can handle them quite easily. They are:

1. To run the script, make sure it is accessible via the same path on each computer running ADU&C (required only on the computers which run it). You can put it on a share, and I think it will work (haven’t tested it), or you can put it on a local directory, but make sure other computers from which you would want to run this option, have this script in the same directory (same path).

2. The script / GUI does not understand the option "Cancel", although it’s there. If you pick "Cancel", you get to actually select "0". Be aware of it.

3. The script requires resolution per OU. It means that it’s easier to move the users sharing the same mailbox store into the same OU, at least for the purpose of running the script. You could create an OU under an existing OU, and move only the users sharing the same mailbox store into it, obtaining the GPO and settings propagated to it from above.

4. There is no "uninstall" option. Don’t want it? Don’t use it. Can’t remove it unless you know what you’re doing.

I tend to believe these flaws/bugs/issues will be dealt with someday, but for the minor usage I had, it was enough, and even better.

By the way – so far, this trick cannot be used for Public Folders, as their information is hidden well too deep. Maybe someday.