Write-cache problems

I wrote this script to turn manipulate the write-cache for anyone interested.

#!/bin/bash
# Disk write-cache utility for ReadyNAS
# By B Goodheart Jan 2012
# V 1.0

# Check we're running as a privileged user
if [ $(id -u) -ne  0 ]
then
	echo "$0: insufficent permissions"
	exit 2
fi

usage () {
	echo "Usage: $0 [-qh] [0|1|on|off|status] [/dev/??]"
			cat << USAGE

A utility for manipulating and querying the write-cache feature for attached disk drives.

Arguments are as follows:
-q		quite mode
-h		prints help and usage information
0 or on		turn write-cache off for all disks or a specified disk
1 or off	turn write-cache on for all disks or a specified disk
status		prints current status of all disks or a specified disk
/dev/??		execute this command for the specified disk only

CONDITIONS:
1) No arguments given is the same as specifying argument "status"
2) User must have root privileges to execute this command
3) If no disk argument is specified, this command will process execution for ALL disks
4) This command does not process USB attached disks

USAGE
}

checkdev() {
	if [ ! -e $1 ]
	then
		echo "$1: no such device"
		exit 1
	fi
}
	
status () {
	disk=$1
	# read the write-cache status for all attached disks in the ReadyNAS disk enclosure
	if [ "$disk" = "all" ]
	then
		for i in /sys/block/[hs]d?; do
			# ignore USB connected disks
			readlink $i | grep -q usb && continue
		
			dev="/dev/`basename $i`"
			echo "${dev}: `/sbin/hdparm -W ${dev} | grep caching`"
		done
	else
		readlink $disk | grep -q usb && return
		checkdev ${disk}
		echo "${disk}: `/sbin/hdparm -W ${disk} | grep caching`"
	fi
}

process () {
	state=$1
	disk=$2
	qflag=$3
	if [ "$disk" = "all" ]
	then
		for i in /sys/block/[hs]d?; do
			# ignore USB connected disks
			readlink $i | grep -q usb && continue
		
			dev="/dev/`basename $i`"
			/sbin/hdparm -${qflag}W${state} ${dev}
			#echo "/sbin/hdparm -${qflag}W${state} ${dev}"
		done
	else
		readlink $disk | grep -q usb && return
		checkdev ${disk}
		/sbin/hdparm -${qflag}W${state} ${disk}
		#echo "/sbin/hdparm -${qflag}W${state} ${disk}"
	fi
	/usr/bin/update_disk_info_cache
}

device="all"
if [ $# = 0 ]
then
	status $device
	exit 0
fi

quiet=""
while getopts qh opt
do
	case "$opt" in
		q)
			quiet="q"
			shift
			;;
		h|\?)
			usage
			exit 0
			;;
	esac
done

#if [ "$1" = "-q" ]
#then
#	quiet="q"
#	shift
#fi

if [ $# = 2 ]
then
	device=$2
fi

case "$1" in
	0|1)
		process $1 $device $quiet
        ;;
        on)
                process 1 $device $quiet
        ;;
        off)
                process 0 $device $quiet
        ;;
        status)
                status $device
        ;;
        *)
                usage
                exit 1
        ;;
esac
exit 0

Examples:
Query the write cache status for all disks:

MainStore:~# hdwritecache
/dev/sda:  write-caching =  1 (on)
/dev/sdb:  write-caching =  1 (on)
/dev/sdc:  write-caching =  1 (on)
/dev/sdd:  write-caching =  0 (off)
/dev/sde:  write-caching =  0 (off)

Query the write cache for a specified disk:

MainStore:~# hdwritecache status /dev/sdd
/dev/sdd:  write-caching =  0 (off)

Turn the write cache off for all disks quietly:

MainStore:~# hdwritecache -q 0
MainStore:~# hdwritecache
/dev/sda:  write-caching =  0 (off)
/dev/sdb:  write-caching =  0 (off)
/dev/sdc:  write-caching =  0 (off)
/dev/sdd:  write-caching =  0 (off)

Turn the write cache on for /dev/sdc:

MainStore:~# hdwritecache 1 /dev/sdc

/dev/sdc:
 setting drive write-caching to 1 (on)
 write-caching =  1 (on)
MainStore:~# hdwritecache 
/dev/sda:  write-caching =  0 (off)
/dev/sdb:  write-caching =  0 (off)
/dev/sdc:  write-caching =  1 (on)
/dev/sdd:  write-caching =  0 (off)