Using the Seagate FreeAgent as a (periodic) Mirror Backup

I recently purchased a Seagate FreeAgent 100D USB drive. The drive is quite nice, small, quiet, and has advanced power management. I plugged the device in on a Fedora 7 installation, and it came right up.

The first problem I had was the NTFS partition that came on the device. This is easily fixed with fdisk and mkfs.ext3. Don't forget to use e2label, especially if you have more than one of the same device.

The next thing you want to do is determine the "id" of the device, so that you can uniquely identify it. The problem is that udev sets up devices in order of connection (/dev/sda, /dev/sdb, ...). To remedy this, use the symbolic links that udev creates under /dev/disk/ to identify the disk by one of the following means:

• /dev/disk/by-id/ - Uses connection, make, model, and serial number


• /dev/disk/by-uuid/ - Uses the UUID given to the partition when it was created


• /dev/disk/by-label/ - If you have used e2label, this is more meaningful than the UUID


• /dev/disk/by-path/ - This is the one you do not want to use!

I want to disable normal users (including myself) from modifying the contents of the backup, so the plan is to keep it unmounted and disable users from mounting it. Thefefor, this is the appropriate entry for me in /etc/fstab:

/dev/disk/by-id/usb-Seagate_FreeAgentDesktop_30DFK39D-0:0-part1 /media/FreeAgent        ext3    defaults        1 2

Note this will require the device to be present and consistent at boot-time. If you don't need this, change the last two numbers in the fstab entry to zero.

Before automating backup, I had a problem: The drive spins down automatically, so if you use only a command like rsync it may terminate due to an I/O Error because it simply timed out. This happened with me using ls, but it doesn't always happen -- so you should be more paranoid about the power mode.

The solution is to use a utility called sdparm, which is made to control SCSI (and SATA) disks. This is available for Fedora in a yum package called simply sdparm. This allows you to send a command to the drive to "start" (spin up) or "stop" (spin down).

Then, the final task is to create a backup procedure that is invoked by crond. Rather than writing something to /etc/crontab, I added the following file to /etc/cron.daily/. Make sure it has execute permissions, and call it (as root) a couple times to make sure it's working.

#!/bin/sh
#
# Backup to a USB disk 
#

# Env variables 
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# OK to change these
LOGFILE=/var/log/backup-usb.log
DISKDEVICE=/dev/disk/by-id/usb-Seagate_FreeAgentDesktop_30DFK39D-0\:0
DISKPARTITION=$DISKDEVICE-part1
MOUNTPOINT=/media/FreeAgent

# Leave these alone
DEVICEFILE=`readlink -f $DISKDEVICE`
PARTITIONFILE=`readlink -f $DISKPARTITION`

# Close stdout
1>&-;
# Close stderr
2>&-;

# Log needs to be rotated manually
#mv $LOGFILE $LOGFILE.1

# Direct stdout and stderr to logfile
exec 1>>$LOGFILE;
exec 2>>$LOGFILE;

echo Begin $0, `date`;

# Preliminary work (get backup device online)
if [ -e $DISKDEVICE ] ;
then
 echo "Device exists (is connected).";

# /usr/bin/sdparm --all $DISKDEVICE

 echo "Sending start (wake up) signal...";
 /usr/bin/sdparm --command=start $DISKDEVICE
 if [ "$?" -eq "0" ] ; 
 then 
  echo "Success";
 else 
  echo "Failed to start device";
  exit;
 fi

 # Get backup partition mounted
 if [ `grep $PARTITIONFILE /etc/mtab | wc -l` -le "0" ] ;
 then
  echo "Device $PARTITIONFILE is not mounted!";
  mount $PARTITIONFILE $MOUNTPOINT;
  if [ "$?" -eq "0" ] ;
  then
   echo "Mounted OK.";
  else
   echo "Failed to mount.";
   exit;
  fi
  
 else 
  echo "Partition $PARTITIONFILE is already mounted.";
 fi
else
 echo "Device doesn't exist, must not be connected!";
 exit;
fi

# Backup procedure 
# 
# For now I'm just using RSYNC because these files don't often change
# 
rsync --verbose --itemize-changes \
--archive --hard-links --partial --delete-before \
/opt/srv/ $MOUNTPOINT/srv/ && \
date && \
df -h $MOUNTPOINT && \
echo ;

# NOTE might also want to un-mount the device at this point 
# to prevent users from modifying it directly !
echo "Unmounting $PARTITIONFILE"
umount $PARTITIONFILE
echo "Stopping device $DISKDEVICE"
/usr/bin/sdparm --command=stop $DISKDEVICE
# /usr/bin/sdparm --all $DISKDEVICE && \

echo End $0, `date`;

The variables section and the rsync command have to be updated to fit your installation and your backup scheme.

Again, this worked well for me, you may have to make adjustments.