MFDigital CD DVD Information Library
Thursday, June 23, 2005
Using CD and DVD writing devices for data backup
Over the past 20 years, tiny plastic discs have completely altered the way we store and access information. These discs rely on technology that was first introduced in the early 70s - on the laser light. CD-R and CD-RW discs have already become the "floppy disk" of personal computing at the start of this century, and there is every indication that DVD may take over that role in the relatively near future.
CD-R is short for "CD-Recordable". Recordable CDs are WORM (Write Once, Read Multiple) media. A single CD disc holds the equivalent of 450 floppy discs at a time. Its capacity is either 650MB or 700MB. In some cases, you can write to a CD-R disc more than once - creating multiple sessions on the same disc - but not all drives can read these discs. And in any case, when the CD-R disc is full, you can't erase the data from it for reuse once it has been written. CD-RW discs and drives (CD-Rewritable) were created to address this limitation: they allow erasing discs and reusing them. CD-Rewritable drives are able to write both CD-R and CD-RW discs.
DVD is a new generation of optical disc storage technology. DVD is essentially a bigger and faster CD: a single DVD disc holds 4.75 GB of data. This is roughly seven times more than you can fit on a CD. DVD became the most successful consumer electronics product of all time in less than three years of its introduction. There are two main DVD formats: "dash" (DVD-R/RW) and "plus" (DVD+R/RW). There is not much difference between them. They both record data and video, and they both read back data and play back video. Both formats are available as recordable drives for computers and as home video recorders. In spite of claims that one format is more compatible with players and drives, both formats are similarly compatible. The biggest thing to worry about is that DVD-RW drives only record on -R and -RW discs, and DVD+RW drives only record on +R and +RW discs, so you have to make sure you get the right kind of blank discs. As time goes by, the different formats are becoming more compatible and more intermixed. By the way, there are DVD-/+RW drives - dual-format, or "combo" drives that write both formats.
Both CD and DVD are great as storage for data backups. It is easy to have a backup copy at hand, because you can take the disc with you wherever you go and restore your files on any computer. If your backup contains confidential information you can save backups onto CD or DVD discs and store them in your personal safe. By storing a copy of your files on CD or DVD discs, you may save your own computer resources: disk space on your local drives or your company servers. Today's CD-Rs that are dirt-cheap, so you only need to find good backup software capable of writing to CD or DVD and you can feel safe about your data.
Various backup programs support different CD and DVD formats mentioned above. Of course, the more formats a program supports, the better for you. You can use either blank (brand-new) discs, or ones already containing some files. In case a disc is not blank, you can either record additional session on it, or erase it if it is rewritable.
When erasing discs you usually have two options: full and quick erase. Full erase, as its name implies, means that all data will be deleted. Quick erase deletes only file system information; it does not delete the data itself, so if you want to securely destroy all previous information, you should choose the full method, otherwise the quick method is the best, because it works much faster.
Usually you can choose the speed for burning your CD or DVD discs. If you select greater speed, the process will take less time, however depending on your writing device and the quality of the media, writing with low speed may result in a more reliable copy. Some backup programs also perform CRC verification. This is an additional validity check used to make sure that the newly created backup copy is readable.
If your backup copy is rather large and its size exceeds free space available on a single disc, you may want to use disc spanning: the procedure of splitting a large file into several parts to store them on several discs. If you want to restore a file that was backed up using disc spanning, and you do not know exactly which disc contains this file, you can insert any disc. If the backup program does not locate required file on that disc, it will prompt you to insert the next span until the file is found.
With today's immense amount of information and the necessity to back up a lot of data, it is often useful to compress the backup copy before saving it on a disc. Many backup programs support widely used ZIP compression. Some programs will also allow you to choose the compression quality. The higher is the compression quality, the more time will be required to process the data, but the resulting ZIP file will be smaller.
Depending on your needs, you can either compress each file separately, or put all files into a single ZIP archive. However, if you want to perform incremental backups adding only new and changed files each time, it is not recommended to put all files into a single ZIP archive, because it is impossible to insert new data to an old ZIP file. So in this case, the backup will be fully rebuilt each time.
After you have saved your files to CD or DVD media, there appears an important question - where to keep the discs with backup copies. If removable-media backups are stacked next to the computer, a fire or other disaster can destroy both at the same time. A secure off-site location is the best. At the very least, you should securely store the discs as far from your computer as possible.