# RootPrompt.org   Nothing but Unix.[Home] [Features] [Programming] [Mac OS X] [Search]


 Feature: Backing up to CD

Noel tells us how he uses a CD-R to backup his home machine.

"Each brand of CD-R uses different chemical compounds for the CD for patent reasons so I would recommend that you use different brands for your backup. That way if one brand degrades faster than it should you will still have your backups."

 (Submitted by Noel Wed Sep 20, 2000 )

  

Backing up to CD

noeld@rootprompt.org

A CD-R(W) is an inexpensive device, with inexpensive media. The one I have was purchased for $135 and I have media that I payed about 33 cents a piece for. A CD-R holds enough information for my personal needs and it is stable compared to magnetic media. I have chosen to use CD-Rs rather than CD-RW because of the additional cost of CD-RWs.

CD-Rs would not be big enough for a backup device in most production shops as it does not hold a great deal of data. Leaving some room for overhead on a Joliet CD you can expect about 620MB of data to fit. This is plenty of room for my home directory and the most important system files, but if you had hundreds of Gigabytes to backup you would need a tall stack of CD-Rs.

If you had too much data to fit on one CD you could break up your backup job into several different CD-Rs. Backup your system on Monday, your MPEGS on Tuesday, your email on Wednesday, etc.

One additional concern is that the cheap CD-Rs may not last as long as the more expensive ones. What I plan to do is use a more expensive CD-R occasionally so that even if the cheap ones fail or only last a year I will still have a backup. Each brand of CD-R uses different chemical compounds for the CD for patent reasons so I would recommend that you use different brands for your backup. That way if one brand degrades faster than it should you will still have your backups.

I am not going to go over setting up your CD-R drive. For help on doing that take a look at the CD Writing HOWTO. I will touch on the command line utility we are going to use to burn the CD-R.

If all you have used is the GUI tools such as cdrtoaster then you may not know the device parameter for cdrecord. You can find this value by using 'cdrecord -scanbus'.

# cdrecord -scanbus
Cdrecord 1.8 (i686-pc-linux-gnu) Copyright (C) 1995-2000 Jorg Schilling
Using libscg version 'schily-0.1'
scsibus0:
        0,0,0     0) 'IOMEGA  ' 'ZIP 100         ' '23.D' Removable Disk
        0,1,0     1) 'MITSUMI ' 'CR-4804TE       ' '2.8C' Removable CD-ROM
        0,2,0     2) *
        0,3,0     3) *
        0,4,0     4) *
        0,5,0     5) *
        0,6,0     6) *
        0,7,0     7) *
# 
The device parameter would be "0,1,0".

The basic steps for this backup are:

  • Collect what we want on the CD-R.
  • Create an image of the CD-R on the hard disk
  • Burn the image onto the CD-R

A simple backup script:

BackupCD.sh

#!/bin/sh

cd /

# Set a couple of values

DATE=`/bin/date +%b-%d-%y`
HOST=`hostname`


echo "Starting Backup"

/bin/date

date >/work/backup/$HOST-$DATE

# Tar the system stuff and place a list on the CD-R

tar -czvf /work/backup/system.tgz \
          ./etc \
          ./usr/local/bin \
                          >/work/backup/system.txt

echo "Building CD Image"
/bin/date

mkisofs -r -f -o /work/cdroms/backup.iso \
                 /home \
                 /work/backup/system.tgz \
                 /work/backup/$HOST-$DATE \
                 /work/backup/system.txt

echo "Burning CD"
/bin/date

cdrecord -v speed=2 dev=0,1,0 -data /work/cdroms/backup.iso

rm /work/backup/system.*

echo "Done"

/bin/date

eject cdrom

Using a CD-RW to backup your system can be an economical method as long as the data you need to backup will fit on a CD-R or you are willing to break the backup into CD-R sized chunks.


Our content can be syndicated: Main page Mac Page

Copyright 1999-2005 Noel Davis. Noel also runs web sites about sailing and kayaking.
All trademarks are the property of their owners.
All articles are owned by their author