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 (up to 8.5 GB) and CD media (up to 800 MB); some have Combo drives that can read from DVDs and write to CDs.
Meanwhile, new standards continue to emerge. Most notably, several third-party vendors are now selling Mac-compatible Blu-ray Disc optical drives with up to 50 GB capacity; higher-capacity Blu-ray media and drives are under development. (The competing HD DVD standard was abandoned in early 2008.) At the moment, however, the cost of Blu-ray drives for Macs is quite high—and out of proportion to their increased capacity.
Historically, Apple has regularly upgraded SuperDrives to support higher-capacity standards. For example, starting in mid-2005, some Macs included SuperDrives that could read and write to double-layer (8.5 GB) DVD+R discs, and by late 2006, all new SuperDrives had this capability. Apple has not yet shipped any SuperDrives with Blu-ray support, but I wouldn't be surprised to see this in the future. See Optical Media Types, next page, 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.
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 reason—and 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.
Table 4-1. Optical Media Types
Name | Capacity | Rewritable? | Use with Combo Drive | Use with SuperDrive |
|---|---|---|---|---|
CD-ROM | up to 800 MB | No | Read-only | Read-only |
CD-R | 650, 700, or 800 MB | No | Yes | Yes |
CD-RW | 650, 700, or 800 MB | Yes | Yes | Yes |
DVD-ROM | up to 4.7 GB | No | Read-only | Read-only |
DVD-R | 4.7 GB | No | Read-only | Yes |
DVD-RW | 4.7 GB | Yes | Read-only | Yes[a] |
DVD+R | 4.7 GB | No | No | Yes[b] |
DVD+RW | 4.7 GB | Yes | No | Yes[c] |
DVD+R DL (double-layer) | 8.5 GB | No | No | Yes[d] |
DVD-RAM | up to 9.4 GB | Yes | No | No |
Blu-ray Disc (BD-R/BD-RE/BD-ROM) | up to 50 GB | BD-ROM: No BD-R: No BD-RE: Yes | No | No |
[a] Except on very early SuperDrive models. Although the Finder does not support DVD-RW media on older SuperDrives, some third-party software may. [b] All SuperDrives shipped in 2005 and later included DVD+R and DVD+RW support. [c] All SuperDrives shipped in 2005 and later included DVD+R and DVD+RW support. [d] Apple began phasing DVD+R DL support into SuperDrives in 2005, and all new SuperDrive-equipped Macs released since late 2006 have had DL capabilities. | ||||
Tip
Not sure which kinds of media your Mac's optical drive can
record onto? Open System Profiler (in /Applications/Utilities) and select Disc
Burning in the list on the left.
A list of supported media types will appear after the labels CD-Write (for CD formats) and DVD-Write (for DVD formats). (In this list, "DL" stands for double-layer.)
CDs (including CD-R and CD-RW) make a poor choice for duplicating your entire hard drive. The highest-capacity CDs you can buy—which, by the way, may or may not be compatible with your hardware and software—hold 800 MB. (Standard CDs hold either 650 or 700 MB.) You would need four to six discs to back up even the smallest possible installation of Mac OS X—not counting all your personal files. And if you want to duplicate a full 120 GB hard disk, that will require upward 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 files—the 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, later).
Recordable DVDs may all look alike, but they vary in format and capacity. (See Optical Media Types, on the previous page, 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 standards—DVD+R and DVD+RW—is supported by currently shipping SuperDrives and most third-party external DVD recorders. In addition, newer third-party drives—and SuperDrives in most Macs shipped from mid-2005 on—can use double-layer DVD+R media with a capacity of 8.5 GB (a single-layer DVD can hold up to 4.7 GB).
Note
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 rewritable (RW) format, it also supports the corresponding write-only recordable (R) 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. And third-party drives using the Blu-ray Disc format can put as much as 50 GB on a disc.
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) discs—if 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, while Blu-ray discs are still quite pricey (a single rewritable 50 GB disc can run upwards of $50).
But there's a catch—several catches, in fact:
Even the highest-capacity recordable DVDs may not be able to store the entire contents of your hard disk.
In cases where you can duplicate your entire hard disk onto a DVD, you will still, in general, be unable to boot from the DVD. As with CDs, you must restore the duplicate onto a hard disk first.
Erasing rewritable DVDs (DVD-RW, DVD+RW, and Blu-ray) can be time-consuming.
With proper care, CDs and DVDs you record should still be readable years or even decades from now. However, I must emphasize the word should. Many people, including me, have had the unpleasant experience of trying to read an old optical disc and finding that over time, its data had become corrupted. Although any CD or DVD—including prerecorded commercial discs—can theoretically lose data, the risks are greater with recordable discs, which use different technologies for storing information.
One set of dangers comes from physical damage. If you expose a disc to heat, humidity, or bright sunlight, or if you bend or scratch the disc, it can physically degrade in such a way that some or all of its data can't be read. But another danger comes from the disc itself. Depending on the materials used, the manufacturing process, and numerous other variables over which you have no control, even discs that are treated with the utmost care can sometimes warp, peel apart, or otherwise deteriorate over the course of several years. Either way, even a disc that looks perfectly good can suffer from subtle corruption that makes it unusable.
Although there are no ironclad guarantees when it comes to the longevity of physical media, I can recommend several steps that will greatly minimize your risks when using optical discs:
Make extra copies. If the chance of a single disc losing data is small, then the chance of two copies both losing data is much smaller. Time and money permitting, keep duplicates of your backup discs—and store the two sets in different locations.
Avoid rewritable discs. Although you'll use more recordable discs (CD-R or DVD±R) than rewritable discs (CD-RW or DVD±RW), each time you erase and rewrite a disc you introduce another chance for data errors and physical damage to creep in. All other things being equal, recordable discs are somewhat safer.
Handle with care. For best results, store your media in its plastic case, upright, in a cool, dark, dry place. Be careful to avoid scratches or fingerprints. And, although I personally consider this overkill, if you want to avoid any possibility of damaging the disk by writing on it or labeling it, you can label the case instead.
Periodically re-record your discs. If you want to keep your backups on disc indefinitely, then every 2–3 years, take your discs out of storage and make copies of them on fresh media.
Archive onto…hard drives. There's an alternative to re-recording your discs periodically. This may sound backwards, but since hard drives are becoming cheaper all the time, and likely will last much longer (if not being actively used) than recordable optical discs, you could copy your CDs and DVDs onto a hard drive (stored as disk images, perhaps, using Disk Utility), and just put the drives away in a safe place.
Buy quality media. Although the quality of optical media doesn't necessarily correlate with its price, it's true that some generic media is manufactured using inferior materials and techniques. Using name-brand media is a better bet. Based on numerous reports I've read, two brands with particularly good track records are TDK Professional and MAM (formerly Mitsui). The MAM discs have their reflective layer made out of 24-karat gold, rather than the more usual silver, and are reputed to be highly resistant to deterioration.
I believe the best backup strategy is the one that requires the least manual effort. Because optical media tend to require a lot of manual effort—and because they do not provide you with a bootable backup—they'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:
For minimum inconvenience, use the highest-capacity discs your drive supports (i.e., DVD rather than CD).
If saving money is paramount, use rewritable media (DVD-RW or DVD+RW), if your drive and software support it. (But also check out Internet Backup Services, which may be comparable in cost.)
Because incremental duplicates are impossible with optical media, plan on making a duplicate just once a month.
A Reminder about Redundancy
As I suggested earlier in Keeping Multiple Backups, no matter which type of backup medium you use, you should always keep multiple copies of your backups. That means multiple hard drives or multiple sets of discs—with one copy stored nowhere near your computer. There's always the chance that a single backup will suffer the same fate as your hard drive: a random failure of some sort. If you try to restore files from a backup and find that it's damaged, you'll be grateful that you had a spare copy. I discuss off-site backups later on, under Mind Your Media.