#!/usr/bin/ruby

# This Ruby script uses sg3_utils (http://sg.torque.net/sg/) to
# automatically put a SCSI device into standby mode after
# a configurable idle time period. This also works with USB
# storage devices (tested with Linux Kernel 2.6.14, sg3_utils 1.11
# on Gentoo Linux with an NEC PCI USB 2.0 controller
# and an external Samsung SP2514N hard disk in an ICY Box.

# Author: Steffen Rusitschka
# Version: 0.1
# Homepage: http://rusi.is-a-geek.org

# time in seconds of device inactivity until it will be 
# put to standby mode (15 minutes)
IDLE_UNTIL_STANDBY = 15 * 60

# device to use
DEVICE = "sda"


lastRequestCount = 0
lastAccessTime = 0
sleepTime = 0

while true
  f = File.open('/sys/block/' + DEVICE + '/device/iorequest_cnt', 'r');
  requestCount = f.readline.chomp.hex
  f.close
  now = Time.now.to_f

  if requestCount != lastRequestCount
    lastAccessTime = now
  end

  # if we are after the timeout and there were new
  # accesses after the last sleep time -> go to sleep (again)
  if now > lastAccessTime + IDLE_UNTIL_STANDBY \
        && lastAccessTime > sleepTime

    sleepTime = now
    system '/usr/bin/sg_start 0 -pc=3 /dev/' + DEVICE

    # increase the request count by one for the command we just sent
    requestCount += 1
  end

  lastRequestCount = requestCount

  # sleep 1 minute
  sleep 60
end