Add script for moving a backup task rather than a host

For machines like nest-backup and cerebro-backup we have lots of backup
tasks for the same host spread across several zpools, so
move-machine-to-zpool.sh can't be used to migrate the contents of a
failing zpool/disk. This adds a script to move an individual ZFS which is
the target of a backup task to another zpool.

It assumes all necessary parent ZFSes already exist on the target. If
they don't it fails.

It does not yet clean up the old ZFS as it's not had a lot of use.

ROOT/usr/lib/chem-zfs-backup-server/move-backup-to-zpool.sh

+#!/bin/bash
+# To move a backup task onto a new zpool
+# This is for use on machines like nest-backup, cerebro-backup where there are multiple
+# backup tasks for each host so move-machine-to-zpool.sh doesn't work. 
+# It assumes the required parent ZFSes exist on the new zpool . 
+
+# Load some settings
+. /etc/default/zfs-backup
+
+function dosql() {
+ SQL="$1"
+ psql -t -c "$SQL"
+}
+
+# 
+if [ -z "$1" ] ; then
+ echo Usage: $0 zfsname [new-zpool]
+ echo Moves the backup in zfsname onto a new zpool
+ echo If the new-zpool parameter is empty, the one with the most space will automatically be chosen
+ exit 1
+fi
+
+SOURCE=$1
+OZ=${SOURCE%%/*}
+
+# Which target is it?
+if [ -z "$TGT" ] ; then
+ echo Finding a target ZFS automatically
+ ZPOOL=`zfs list -H -oname -S avail -d0 | grep -v zroot | grep -v $OZ | head -n1`
+ NZ=$ZPOOL
+fi
+
+TGT=${SOURCE/$OZ/$NZ}
+
+echo moving $SOURCE to $TGT
+set -e
+RUNNING=`dosql "select count(*) from backup_log natural join backup_task where zfs_target='$SOURCE' and ended_processing is null and started_processing is not null"`
+RUNNING=`echo $RUNNING` # chomp
+#echo RUNNING $RUNNING
+if ! [ "$RUNNING" = 0 ] ;  then
+ echo $SOURCE has a job running
+ exit 3
+fi
+
+# Disable this host
+dosql "update host set disabled='t' from backup_task where zfs_target='$SOURCE' and backup_task.host_id = host.host_id;"
+# De-queue jobs for this host
+dosql "delete from backup_log where backup_task_id in (select backup_task_id from backup_task where zfs_target='$SOURCE') and ended_processing is null and started_processing is null;"
+
+# Update tasks
+dosql "update backup_task set zfs_target=regexp_replace(zfs_target,'^$SOURCE','$TGT') where zfs_target ='$SOURCE'";
+
+
+# Move ZFS
+TIME=`date +%s`
+zfs snapshot -r $SOURCE@$TIME
+zfs hold zfs-moving $SOURCE@$TIME
+SIZE=`zfs list -H -o used $SOURCE`
+echo Sending  ZFS [ $SIZE]
+zfs send -R $SOURCE@$TIME | mbuffer | zfs receive -F $TGT
+
+# Re-enable host
+echo Re-enabling backup task
+dosql "update host set disabled='f' from backup_task where zfs_target='$TGT' and backup_task.host_id = host.host_id;"
+# Tidy up
+#echo Removing old ZFS, snapshots etc
+#for SN in `zfs list -r -t snapshot -H -o name $SOURCE/$FQDN ` ; do for H in `zfs holds -H $SN | awk ' { print $2 ; } '` ; do zfs release $H $SN ; done ; done
+#zfs destroy -r $SOURCE/$FQDN