dramatically speed up Time Machine backups on OS X

speedy_tm.sh

#!/bin/sh

# Turns off low priorioty throttling while Time Machine backups are in progress.
#  Also prevents sleeping/idling while TM is running
# 
# by https://github.com/popmonkey
# 
# to truly automate this, add the following to /etc/sudoers (sudo visudo)
#  (remove one set of # and change 'user' to your username)

# # allow speedy_tm to set throttle
# user ALL=(root) NOPASSWD: /usr/sbin/sysctl debug.lowpri_throttle_enabled=1
# user ALL=(root) NOPASSWD: /usr/sbin/sysctl debug.lowpri_throttle_enabled=0

# and maybe even run it on boot

LAST_PHASE=
log() {
    echo "[$(date)] $@"
}

is_tm_running() {
    CURRENT_PHASE=$(tmutil currentphase)
    if [[ $LAST_PHASE != $CURRENT_PHASE ]]; then
        log Phase: $CURRENT_PHASE
        LAST_PHASE=$CURRENT_PHASE
    fi

    if [[ $CURRENT_PHASE == "BackupNotRunning" ]]; then
        return 1
    else
        return 0
    fi
}

set_throttle() {
    CURRENT_VAL=$(sysctl debug.lowpri_throttle_enabled | awk '{ print $2 }')
    if [[ $1 != $CURRENT_VAL ]]; then
        log changing lowpri throttle to $1
        sudo sysctl debug.lowpri_throttle_enabled=$1
    fi
}

ctrl_c() {
    log "CTRL-C trapped"
    set_throttle 1
    exit 0
}

trap ctrl_c INT

while : ; do
    if is_tm_running; then
        set_throttle 0
        # prevent system from sleeping
        caffeinate -i sleep 29 &
    else
        set_throttle 1
    fi

    sleep 30
done