Add a periodic zfs scrub script.

Features:
 - configurable amount of days between scrubs (default value or per pool)
 - do not scrub directly after pool creation (respects the configured
   number of days between scrubs)
 - do not scrub if a scrub is in progress
 - tells how to see the status of the scrub
 - tells how many days since the last scrub if it skips the scrubbing
 - warns if a non-existent pool is specified explicitely
   (default: no pools specified -> all currently imported pools are
   handled)
 - runs late in the periodic run to not slow down the other periodic daily
   scripts

Discussed on:	fs@

etc/periodic/daily/800.scrub-zfs

@@ -0,0 +1,86 @@
+#!/bin/sh
+#
+# $FreeBSD$
+#
+
+# If there is a global system configuration file, suck it in.
+#
+if [ -r /etc/defaults/periodic.conf ]
+then
+    . /etc/defaults/periodic.conf
+    source_periodic_confs
+fi
+
+: ${daily_scrub_zfs_default_threshold=30}
+
+case "$daily_scrub_zfs_enable" in
+    [Yy][Ee][Ss])
+	echo
+	echo 'Scrubbing of zfs pools:'
+
+	if [ -z "${daily_scrub_zfs_pools}" ]; then
+		daily_scrub_zfs_pools="$(zpool list -H -o name)"
+	fi
+
+	for pool in ${daily_scrub_zfs_pools}; do
+		# sanity check
+		zpool list ${pool} >/dev/null 2>&1
+		if [ $? -ne 0 ]; then
+			echo "   WARNING: pool '${pool}' specified in"
+			echo "            '/etc/periodic.conf:daily_scrub_zfs_pools'"
+			echo "            does not exist"
+			continue
+		fi
+
+		# successful only if there is at least one pool to scrub
+		rc=0
+
+		# determine how many days shall be between scrubs
+		eval _pool_threshold=\${daily_scrub_zfs_${pool}_threshold}
+		if [ -z "${_pool_threshold}" ];then
+			_pool_threshold=${daily_scrub_zfs_default_threshold}
+		fi
+
+		_last_scrub=$(zpool history ${pool} | \
+		    egrep "^[0-9\.\:\-]{19} zpool scrub ${pool}\$" | tail -1 |\
+		    cut -d ' ' -f 1)
+		if [ -z "${_last_scrub}" ]; then
+			# creation time of the pool if no scrub was done
+			_last_scrub=$(zpool history ${pool} | \
+			    sed -ne '2s/ .*$//p')
+		fi
+
+		# Now minus last scrub (both in seconds) converted to days.
+		_scrub_diff=$(expr -e \( $(date +%s) - \
+		    $(date -j -f %F.%T ${_last_scrub} +%s) \) / 60 / 60 / 24)
+		if [ ${_scrub_diff} -le ${_pool_threshold} ]; then
+			echo "   skipping scrubbing of pool '${pool}':"
+			echo "      last scrubbing is ${_scrub_diff} days ago, threshold is set to ${_pool_threshold} days"
+			continue
+		fi
+
+		_status="$(zpool status ${pool} | grep scrub:)"
+		case "${_status}" in
+			*"scrub in progress"*)
+				echo "   scrubbing of pool '${pool}' already in progress, skipping:"
+				;;
+			*"none requested"*)
+				echo "   starting first scrubbing (after reboot) of pool '${pool}':"
+				zpool scrub ${pool}
+				;;
+			*)
+				echo "   starting scrubbing of pool '${pool}':"
+				zpool scrub ${pool}
+				;;
+		esac
+
+		echo "      consult 'zpool status ${pool}' for the result"
+	done
+	;;
+
+    *)
+	rc=0
+	;;
+esac
+
+exit $rc

share/man/man5/periodic.conf.5

@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 12, 2007
+.Dd June 15, 2010
 .Dt PERIODIC.CONF 5
 .Os
 .Sh NAME
@@ -611,6 +611,25 @@ when
 .Va daily_queuerun_enable
 is set to
 .Dq Li YES .
+.It Va daily_scrub_zfs_enable
+.Pq Vt bool
+Set to
+.Dq Li YES
+if you want to run a zfs scrub periodically.
+.It Va daily_scrub_zfs_pools
+.Pq Vt str
+A space separated list of names of zfs pools to scrub.
+If the list is empty or not set, all zfs pools are scrubbed.
+.It Va daily_scrub_zfs_default_threshold
+.Pq Vt int
+Number of days between a scrub if no pool-specific threshold is set.
+The default value if no value is set is 30.
+.It Va daily_scrub_zfs_ Ns Ao Ar poolname Ac Ns Va _threshold
+.Pq Vt int
+The same as
+.Va daily_scrub_zfs_default_threshold
+but specific to the pool
+.Va Ns Ao Ar poolname Ac Ns .
 .It Va daily_local
 .Pq Vt str
 Set to a list of extra scripts that should be run after all other