Use Systemd-provided cgroup IO limits

README.man

@@ -63,6 +63,10 @@ you can turn off the automatic repair (\fB\fCBTRFS\_SCRUB\_READ\_ONLY\fR)
 .IP \(bu 2
 the default IO priority is set to \fIidle\fP but scrub may take long to finish,
 you can change priority to \fInormal\fP (\fB\fCBTRFS\_SCRUB\_PRIORITY\fR)
+.IP \(bu 2
+If using systemd timers, you can also enable (`BTRFS_IO_LIMIT`) to set IO resource
+.IP \(bu 2
+limits
 
 .RE
 

README.md

@@ -46,6 +46,8 @@ __Tuning:__
 * you can turn off the automatic repair (`BTRFS_SCRUB_READ_ONLY`)
 * the default IO priority is set to *idle* but scrub may take long to finish,
   you can change priority to *normal* (`BTRFS_SCRUB_PRIORITY`)
+* If using systemd timers, you can also enable (`BTRFS_IO_LIMIT`) to set IO resource
+* limits
 
 __Related commands:__
 

btrfsmaintenance-refresh-cron.sh

@@ -84,6 +84,20 @@ OnCalendar=$PERIOD
 EOF
 			systemctl enable "$SERVICE".timer &> /dev/null
 			systemctl start "$SERVICE".timer &> /dev/null
+			OIFS="$IFS"
+			IFS=:
+      if [ "$BTRFS_IO_LIMIT" = "true" ] ; then
+			  mkdir -p /etc/systemd/system/"$SERVICE".service.d
+				echo '[Service]' > /etc/systemd/system/"$SERVICE".service.d/10-iolimits.conf
+				for DEVICE in $BTRFS_IO_LIMIT_DEVICES ; do
+				  echo "IOReadBandwidthMax=$DEVICE $BTRFS_IO_LIMIT_BW"
+				  echo "IOWriteBandwidthMax=$DEVICE $BTRFS_IO_LIMIT_BW"
+				  echo "IOReadIOPSMax=$DEVICE $BTRFS_IO_LIMIT_IOPS"
+				  echo "IOWriteIOPSMax=$DEVICE $BTRFS_IO_LIMIT_IOPS"
+				done >> /etc/systemd/system/"$SERVICE".service.d/10-iolimits.conf
+				systemctl daemon-reload
+			fi
+			IFS="$OIFS"
 			;;
 	esac
 }

sysconfig.btrfsmaintenance

@@ -152,3 +152,39 @@ BTRFS_TRIM_MOUNTPOINTS="/"
 # the timer for these tasks(s) elapsed while the system was suspended
 # or powered off.
 BTRFS_ALLOW_CONCURRENCY="false"
+
+## Path:        System/File systems/btrfs
+## Description:	Configuration to allow limiting bandwidth and IOPS
+## Type: 	boolean
+## Default:	"false"
+# Maintenance tasks may starve system resources for other more urgent
+# workloads. This enables IO resource limits when using systemd timers.
+BTRFS_IO_LIMIT="false"
+
+## Path:        System/File systems/btrfs
+## Description:	Configuration to specify devices with limited bandwidth and/or IOPS
+## Type: 	string
+## Default:	"/dev/sda"
+# With IO resource limits, this setting specifies the block devices that will
+# have resource limits set
+# (Colon separated paths)
+BTRFS_IO_LIMIT_DEVICES="/dev/sda"
+
+## Path:        System/File systems/btrfs
+## Description:	Configuration to specify IOPS limits
+## Type: 	string
+## Default:	"40"
+# With IO resource limits, this setting specifies the per-device IOPS limits.
+# SSDs can typically perform thousands of operations per second while spindles
+# can only perform up to 120 IOPS, though with terrible throughput.
+BTRFS_IO_LIMIT_IOPS="40"
+
+## Path:        System/File systems/btrfs
+## Description:	Configuration to specify disk bandwidth limits
+## Type: 	string
+## Default:	"20M"
+# With IO resource limits, this setting specifies the per-device bandwidth
+# limit. The typical maximum speed of SATA SSDs is about 550MBps limited by
+# the SATA protocol. Current high-end spindle drives' typical maximum speed
+# is about 240MBps.
+BTRFS_IO_LIMIT_BW="20M"