CD-RW drives are similiar to normal CD drives - they allow reading data from pre-recorded CD disks, and cost $100 to $400. However, they can also write data to special CD media. CD-R media can be written to once, while CD-RW can be written to, erased, formatted, and then written to again - over and over. Both types of media will support writing data in one session, or writing a portion of data to the disk in one session, then writing another portion in a second or later session. Normal capacity of both media is 650MB; however use of multiple session can decrease it to as low as 500MB. New high-capacity CD-RW disks raise the limit to 700MB.Cost of CD-R disks currently range for about $.40 to $1.50, depending on quality and quantity. CD-RW's run $1.00 to $2.50.
Use of current CD-R and CD-RW drive gives two major options for backup of data on your computer. One is to use a file copy program, such as Adaptec's Easy CD Creator. This will allow generation of a CD where files can be copied singly or in groups back to the original computer or another computer.
The second is the use of a standard backup program that will write to a CD-R drive, as well as tape drives and floppy disks. The top program in this area is Veritas's Backup Exec. The advantage of this method is that you can easily use file compression, thereby expanding the disk capacity by a factor of two.
One way around the limited amount of storage space available on a CD-R is to break up the backup into smaller segments, and run one segment each night. Let's say that your system has 5GB of files that you want to backup on a routine basis. By using compression, you should be able to break the data up into five backup sessions of about 1GB each. Set the first one for Monday night, and insert a blank CD into the drive. On Tuesday, check the backup log to assure the backup functioned properly, make sure the second session is scheduled for Tuesday night, and again insert a blank disk. The same method will work for larger data backups - 10GB can be done over a two week period.
Another good method is to do a full backup of the system to multiple disks in one session, and then do differential backups on a routine basis until the next full backup. The first backup contains copies of all of the files. The second contains copies of only those files that have been added or changed since the first full backup was done. The third will also contain copies of only those files that have been added or changed since the first full backup was done.
At MicroMetric this is the type of backup we are currently doing. A full backup is done on a monthly basis, to CD-R media. Then weekly differential backups are done during the month, to two sets of CD-RW media. Working with four computers on a network, with about 14GB of data, the latest monthly backup required 16 disks (each computer is put on its own set of disks) and the differentials took 1-3 disks.
One of CD-RW's major selling points, writing in multiple sessions, is also one of its major problems -- not from a technology standpoint but from a usability standpoint. Users often misunderstand the process of multisession writing, and the software that comes with CD-RW drives is more than a little obscure in this matter. It's hard to know what options to use in order to write to a CD in multiple sessions, because issues such as closing and linking sessions and closing the disk come into play. When you consider that you can use several recording formats, the chances for confusion multiply. A great article on this appeared earlier this year, and can be found at:
http://www.zdnet.com/pcmag/stories/solutions/0,8224,2615601-2,00.html