The various flavors of recordable CDs and DVDs are collectively known as optical media, because they rely on lasers to read and write data to them. Most of the Macs made in the past several years include a SuperDrive, which can write to and read from DVD media (4.7 GB) and CD media (up to 800 MB); some have Combo drives that can read from DVDs and write to CDs.
Apple is constantly upgrading the capabilities of the optical drives in their computers. Starting in mid-2005, some Macs included SuperDrives that could read and write to double-layer (8.5 GB) DVD+R discs. In the future, DVD varieties with even greater capacitysuch as Blu-ray and HD-DVDwill become common, and will probably find their way into new Macs. See Table 2 for an overview of current optical media types.
Because built-in optical drives do not require an additional purchase (except the media, which is relatively inexpensive), it's logical to consider using them for backups. In a few cases they may be adequate, but in general I'd like to steer you away from backing up your Mac onto optical media.
The first thing I should point out is that backing up to any optical media is slow. If you have only a few gigabytes of data to back up, this may not bother you, but as your storage needs increase, you're more likely to find it problematic. True enough, some optical drives are faster than others; a 52x CD burner will obviously require much less of your time than a 2x burner. Even so, the fastest optical drives transfer data at less than one-tenth the speed of the slowest hard drives. And if you're talking about backing up many gigabytes of data, you're still looking at an extremely lengthy process.
Not sure which kinds of media your Mac's optical drive can record on? Open Terminal (in /Applications/Utilities) and enter:
A list of supported media types will appear after the label CD-Write (for CD formats) and DVD-Write (for DVD formats). (In this list, "DL" stands for double-layer.)
Another disadvantage of using your optical drive for backups is that it requires your attention. If your backups run automatically on a schedule, you must make sure a blank disc is in the recorder at the proper time. If you schedule backups for when you're using the Mac (so that you can easily swap discs), you face the possibility that you'll want to use your optical drive for some other reasonand even if not, your Mac may slow down unacceptably during the backup process.
Financial considerations alone make optical media an attractive option, despite their disadvantages. But before you decide on an optical drive as your backup device, consider the following factors.
CDs (including CD-R and CD-RW) make a poor choice for duplicating your entire hard drive. The highest-capacity CDs you can buywhich, by the way, may or may not be compatible with your hardware and softwarehold 800 MB. (Standard CDs hold either 650 or 700 MB.) In order to duplicate your entire hard diskeven with the smallest possible installation of Tigeryou would need four to six discs, depending on their capacity. And if you want to duplicate a full 120 GB hard disk, that will require upwards of 170 discs! Even then, you will not be able to boot from your duplicate; you'd need to restore it to a hard disk first. Because of the number of discs required, the amount of user interaction the backup will require, and the inability to boot from the final product, CDs are a bad idea for duplicates.
When it comes to archive backups, CDs show a bit more promise. Yes, it still takes a stack of them, and yes, that means time-consuming sessions of swapping (and labeling!) discs. However, if you're backing up only your data files (not your entire hard disk)and particularly after your first session, when you're incrementally backing up only changed filesthe time and aggravation it requires will be much less. As CDs go, CD-RW media has an edge over CD-R (even though it's almost twice as expensive) in that it can be erased and reused when your stack of discs becomes too large (see Recycling vs. Long-Term Archives, page 172).
Recordable DVDs may all look alike, but they vary in format and capacity. (See Table 2, page 125, for an overview of the different formats.) Early Apple SuperDrives supported only DVD-R media, though with the right software, you could also use erasable DVD-RW media. A pair of competing standardsDVD+R and DVD+RWis supported by currently shipping SuperDrives and most third-party external DVD recorders. In addition, newer third-party drivesand SuperDrives in most Macs shipped from mid-2005 oncan use double-layer DVD+R media with a capacity of 8.5 GB (a single-layer DVD can hold up to 4.7 GB).
You will sometimes see drives described as supporting "DVD±R" or "DVD±RW." The ± symbol means both + and (as in, DVD+R and DVD-R). And if a drive supports a rewriteable format, it also supports the corresponding write-only format. So, for example, a DVD±RW drive also supports DVD-R and DVD+R.
Another standard, known as DVD-RAM, is also supported by many third-party drives (as well as some older Macs). Depending on the format, a DVD-RAM disc can hold up to 9.4 GB of data.
Despite these differences, recordable DVDs all share the same basic traits: significantly higher capacities than CDs, offset by much slower recording speeds.
First, the good news: if you want the lowest possible cost per gigabyte of storage over the long run, you can hardly do better than DVD-RW (or DVD+RW) discsif your optical drive and software supports them. Buy a package of 50 (typically sold without cases on a plastic spindle) for under $50, and you have enough media to back up a medium-sized hard disk for a couple of years. When all the discs are full, erase them and start again. DVD-R discs, although not erasable, are a bit cheaper than rewritable DVD-RW or DVD+RW media, and will work with any SuperDrive. DVD+R DL discs hold more data, but are not erasable.
But there's a catchseveral catches, in fact:
Final Thoughts on Optical Drives
I believe the best backup strategy requires the least manual effort. Because optical media tend to require a lot of manual effortand because they do not provide you with a bootable backupthey're less than ideal. However, if you've just spent your entire savings on a new iMac and you can't possibly spring for even a single external hard drive, backing up onto optical media is vastly better than not backing up at all. Just keep these thoughts in mind: