Media and Device Types
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## Media and Device Types

Cedar Backup is focused around writing backups to CD or DVD media using a standard SCSI or IDE writer. In Cedar Backup terms, the disc itself is referred to as the media, and the CD/DVD drive is referred to as the device or sometimes the backup device. [13]

When using a new enough backup device, a new “multisession” ISO image [14] 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 — which is really unusual today — 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 CD media:

cdr-74

  74-minute non-rewritable CD media

cdrw-74

  74-minute rewritable CD media

cdr-80

  80-minute non-rewritable CD media

cdrw-80

  80-minute rewritable CD media

I have chosen to support just these four types of CD media because they seem to be the most “standard” of the various types commonly sold in the U.S. as of this writing (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.

Cedar Backup also supports two kinds of DVD media:

dvd+r

  Single-layer non-rewritable DVD+R media

dvd+rw

  Single-layer rewritable DVD+RW media

The underlying growisofs utility does support other kinds of media (including DVD-R, DVD-RW and BlueRay) which work somewhat differently than standard DVD+R and DVD+RW media. I don't support these other kinds of media because I haven't had any opportunity to work with them. The same goes for dual-layer media of any type.

[13] 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.

[14] An ISO image is the standard way of creating a filesystem to be copied to a CD or DVD. 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.

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