Media and Device Types

Cedar Backup is focused around writing backups to CD-R or CD-RW media using a standard SCSI or IDE CD writer. In Cedar Backup terms, the disc itself is referred to as the media, and the CD-R or CD-RW drive is referred to as the device or sometimes the backup device. [14]

When using a new enough backup device, a new “multisession” ISO image [15] is written to the media on the first day of the week, and then additional multisession images are added to the media each day that Cedar Backup runs. This way, the media is complete and usable at the end of every backup run, but a single disc can be used all week long. If your backup device does not support multisession images, then a new ISO image will be written to the media each time Cedar Backup runs (and you should probably confine yourself to the “daily” backup mode to avoid losing data).

Cedar Backup currently supports four different kinds of media:

cdr-74

74-minute non-rewritable media

cdrw-74

74-minute rewritable media

cdr-80

80-minute non-rewritable media

cdrw-80

80-minute rewritable media

I have chosen to support just these four types of media because they seem to be the most “standard” of the various types commonly sold in the U.S. today (early 2005). If you regularly use an unsupported media type and would like Cedar Backup to support it, send me information about the capacity of the media in megabytes (MB) and whether it is rewritable.

Future versions of Cedar Backup may support writable DVDs. [16] Now that I have my own DVD±RW hardware, this will happen when I get some time to work on it and/or when someone else shows interest in it. If you would like to see support for DVDs in Cedar Backup and can offer some help, please write the Cedar Backup Users mailing list. [17]



[14] My original backup device was an old Sony CRX140E 4X CD-RW drive. It has since died, and I currently develop using a Lite-On 1673S DVD±RW drive.

[15] An ISO image is the standard way of creating a filesystem to be copied to a CD. It is essentially a “filesystem-within-a-file” and many UNIX operating systems can actually mount ISO image files just like hard drives, floppy disks or actual CDs. See Wikipedia for more information: http://en.wikipedia.org/wiki/ISO_image.

[16] It would just require a new DvdWriter class in writer.py as well as some minor changes to configuration code. All writer-related access is through an abstract interface, so once the new writer is implemented, the rest of the code will be able to use it without any changes.