Home / Apple / How-To
How-To

What to look for in an external hard drive

By Joe Kissell
Macworld DEC 13, 2009 9:24 pm PST

Editor’s Note: The following article is excerpted from Joe Kissell’s Take Control of Mac OS X Backups, Fourth Edition. It includes two portions of a chapter about backup media: the first portion looks at backing up to a local, external drive and the second has Joe’s overall recommendations for backup media. Take Control of Mac OS X Backups, Fourth Edition is a 196-page electronic book that explains how to create a backup strategy that protects your data and enables quick recovery in case of catastrophe. It is available for $15 from TidBits Publishing.

When it comes to safeguarding your data, I use and suggest external hard drives as a backup medium. In almost every case, I believe they’re the best choice for individuals and small networks.

I deliberately said “external hard drives”—even though you could save some money on the enclosures and extra electronics by buying bare drives that can be mounted inside your desktop Mac Pro or Power Mac. I advocate external drives because:

  • You can disconnect an external drive and store it off-site—an important safeguard against theft.
  • If your computer suffers severe damage due to a power surge, a leaky roof, or being knocked off the desk accidentally, your internal hard drives may fail along with the rest of the machine.

Hard drive virtues

You may feel anxiety about the cost of external hard drives—especially since you should have at least two, and perhaps three of them. They may seem extravagant in a way that DVD-Rs, say, do not. So let me sing the praises of hard drives for a moment, while explaining why they’re not only the best solution, they’re economical too:

• Speed: The first thing hard drives have going for them is speed. You may have hundreds of gigabytes of data on your computer’s internal hard disk, but copying such large amounts of data can be extraordinarily time-consuming under the best of circumstances. Even fast optical drives and tape drives transfer data at a fraction of the speed of a slow hard drive. If you want to do more with your computer than watch it back up your data, you’ll appreciate the time savings a hard drive provides.

• Capacity: If you’re backing up to a medium with less capacity than your hard disk, sooner or later you’ll have to swap media. Even the newest Blu-ray media can’t store the entire contents of a moderately large hard disk on a single disc. Swapping media isn’t the worst thing in the world, but the more often you have to do so, the more of an aggravation backing up becomes. If, on the other hand, you use an external hard drive with sufficient capacity, you’ll never have to swap media—and you can allow your backups to run unattended at any time of the day or night.

• Random access: In addition to raw speed in copying files, hard drives offer the advantage of random access. (Tapes, by contrast, offer only linear access—the drive must fast-forward or rewind to get to any arbitrary piece of data.) Besides using space more efficiently, this means it takes no longer to restore files stored over a period of weeks than it does to restore files stored on a single date.

• Versatility: When you use a hard drive for backups, you can put both duplicates and versioned backups on the same device. You can (usually) boot from it, and even, in a pinch, use it as supplemental storage for other projects. Plus, using a hard drive keeps your optical drive (or other removable storage devices) free for installing software, burning DVDs, or other day-to-day tasks.

• Economy: As I write this, 1TB FireWire/USB combo drives can be found at retail for well under $150, and if you look online at discount stores and eBay auctions, you can find them for even less. (By comparison, when I wrote the first edition of this book in 2004, the going price for a 160 GB hard drive was close to $200.) That’s quite a bargain—especially when you factor in the recurring costs of optical media or tapes.

Further, how much is your time worth? Can you afford to spend an entire day restoring from a stack of CD-ROMs? If, instead, you could be up and running minutes after a drive failure, what would that be worth to you? Based on my own experience, I can say with conviction that an initial investment of a few hundred dollars pays for itself many times over when you consider the time and aggravation it saves in the long run.

Warning: If you have a large internal hard disk and far too little data to fill it, you may be tempted to partition it into several volumes and store backups on each one—instead of using separate physical drives. Although this is marginally better than not backing up at all, it’s still an incredibly bad idea. Hard drives usually don’t die one partition at a time. You could easily encounter a problem that makes it impossible to access any part of the disk, in which case your backups would be useless. And just like a second internal drive, a second partition is vulnerable to theft and damage that affects your entire computer.

Does size matter?

If you’re using a hard drive for backups, how large does it need to be? This seemingly tricky question has a relatively easy answer: as a rule of thumb, a destination volume should have between 1 and 1.5 times the capacity of the source volume. Sometimes one can comfortably store both a duplicate and several months’ worth of a versioned backup on a single disk the same size as the one being backed up—but you can check this with a little bit of math.

Except when backing up to a Time Capsule (in which case you’ll use its disk only for versioned backups and rely on a separate drive for duplicates), I advocate partitioning each backup disk into two volumes—one for a duplicate and one for versioned backups. It’s easy to figure out how much space you need for each, and then add the two amounts together to get a total disk size for the backup drive.

The Finder’s Get Info window for a hard disk. The number next to Used indicates the amount of data currently stored on the volume.
Duplicates: For duplicates, you need a volume that will hold all the data on your disk—which may be much smaller than its actual capacity—and provide extra breathing room. To find out how much space your data currently occupies, select your hard drive’s icon in the Finder and choose File -> Get Info. The figure next to the word “Used” (shown on the right) is the amount of space the data currently occupies.

Assuming that you regularly add new files to your computer, you will want to leave a significant cushion to accommodate the files you’re likely to add during the next 6 to 12 months. If you do not have a good sense of the rate at which your data will grow, multiply the Used figure by 1.5, and then round up to the nearest gigabyte. (In this example, the volume “Leopard” would require at least 487GB for a duplicate.) In any case, your duplicate volume need never be larger than the total capacity of the disk you’re backing up.

Versioned backups: For versioned backups, the situation is slightly different: your backup software may compress your data, saving space; on the other hand, you’ll continually add new and modified files, increasing the space used.

Begin by determining the total space occupied by the data you plan to back up (again, use the Finder’s Get Info command), which could be your entire disk, or perhaps only your home folder if you perform a selective backup. Next, subtract the total size of any folders you intend to exclude (for example, ~/Music/iTunes/iTunes Music). Now multiply this total by 1.5. The resulting figure—let’s call it x—is the minimum amount of space you should allot for a versioned backup partition if you’re using compression. Without compression (and remember, if you’re using Time Machine, it doesn’t compress your backups), multiply x by two.

Note: If you’re backing up several Macs over a network to a single set of media, be sure to perform these calculations for each computer, and then add them together. Although some network backup software can save space by maintaining just one copy of a file that’s identical across multiple computers, you’ll be safer if you ignore that possibility and allow more breathing room.

I hasten to point out that these figures represent recommended minimums. They will enable you to back up your data comfortably today, but as your hard disk fills up, you want a backup disk that can keep up with it. So all things considered, you should buy a backup disk with a higher capacity than what you think you need right now. Given the rapidly falling prices of hard drives, and the decreasing differences between medium- and large-capacity models, it no longer makes sense to get a slightly smaller disk just to save a few dollars. As of mid-2009, desktop drives in the 500GB to 1.5TB range provide, on average, the best value (in gigabytes per dollar), and one or more of those drives will make the most sense for the majority of users.

Choosing a hard drive

Because so many different external hard drives exist, the choice can be daunting. Here’s my quick guide to what you need to know.

Interface: You can get hard drives with almost any combination of FireWire 400, FireWire 800, USB 2.0, and eSATA (external Serial ATA) interfaces. The theoretical speed with which these interfaces can transfer data goes in this order, from slowest to fastest: FireWire 400, USB 2.0, FireWire 800, and eSATA. However, in practice, USB 2.0 is nearly always much slower than either version of FireWire. FireWire 800 can be significantly faster than FireWire 400, but usually not twice as fast, as the number implies—you may see only a modest speed increase. Finally eSATA is unquestionably the fastest, but as of mid-2009, no Macs come with eSATA ports; you have to add them with a third-party PCI or PCI-X card (for Power Mac and Mac Pro models), a PC card (for PowerBooks), or an ExpressCard/34 (for some MacBook Pros). Even then, not all adapters support booting a Mac from an eSATA drive (check with the manufacturer if in doubt).

For most people, FireWire 800 is the best choice (assuming your Mac supports it), followed by FireWire 400 and USB. In any case, be sure to get a drive with at least one interface that matches what’s on your Macintosh. (For example, the MacBook Air has no FireWire ports—just USB 2.0.) If you can afford the slightly higher price, you won’t go wrong with a quad-interface drive, which has USB, both FireWire varieties, and eSATA.

One-touch backups: Maxtor sells OneTouch external hard drives with a button that enables you to launch software and execute a backup just by pressing it. I’d rather have my backups run automatically or on a schedule—one less button to press! (Note: Seagate purchased Maxtor in mid-2006, but the new combined company is keeping the two brands separate for the time being.)

Automatic backups: CMS Products’ ABSplus drives include software that performs a duplicate as soon as you plug in the drive. That’s great—but only part of what we want. I’d opt instead for the flexibility of standard backup software. Feel free to get an ABSplus, but plan to supply your own software, at least for archiving.

Clickfree devices: The Clickfree line of backup devices—which includes everything from credit card-sized flash drives to pocket-sized portable drives to 2TB desktop drives—combines a USB external storage device with built-in software.

The first time you plug the drive into your Mac, you run the included setup program, which requires only a couple of clicks. Thereafter, the drive automatically backs up important files whenever it’s plugged in. No scheduling, configuration, or manual intervention is ever required, but if you need to restore files, you can do so by running the software included on the drive. Although that all sounds marvelous in that it’s incredibly easy to use, bear in mind that Clickfree products provide neither bootability nor versioned backups, my two key pillars of a solid backup strategy. So I suggest resisting the temptation and sticking with conventional drives.

Build-your-own: Numerous companies sell FireWire-, USB-, and/or eSATA-equipped cases into which you can place your own IDE or SATA drive mechanism. If you’re comfortable doing some minor tinkering and bargain hunting, you may be able to save a bit of money this way. (See the next item, also, for an alternative.)

Caseless connector kits: You don’t necessarily need a case to connect a bare drive mechanism to your Mac. Several companies offer adapters that connect various combinations of bare IDE or SATA drives directly to USB or FireWire ports. Although you’ll have to go without the additional protection and ventilation that a case provides (making them best only for short-term use), you can save money and space with one of these. Examples include:

Hot-swappable drive bay enclosures: Several companies, including FirmTek, Granite Digital, and WiebeTech, sell hot-swappable FireWire, USB 2.0, and/or eSATA hard drive assemblies. You get a single case, power supply, and cable, to which you add one or more hard drives, each in a special carrier. You can pop out one drive and pop in another quickly, making it easy to rotate backups. But you pay quite a premium for that small convenience.

Multi-drive enclosures: Another recent trend is enclosures containing two or more non-removable drive mechanisms configured as a RAID in order to appear as a single, larger volume. Examples are Maxtor’s OneTouch III, Turbo Edition and LaCie’s Hard Disk MAX.

Pocket-sized hard drives: If you need to back up large amounts of data while traveling, or if your laptop lacks a CD or DVD burner, consider a pocket-sized hard drive. These drives typically use the same 2.5-inch mechanisms that laptops do, and can often be powered through the FireWire or USB cable, eliminating the need to carry a bulky AC adapter with you. (In fact, I like these drives even for backing up desktop computers, because they’re quieter than full-size drives and require less desk space and cable clutter—albeit at a slightly higher price.) Some examples:

  • LaCie Mobile Drives: LaCie makes several lines of pocket-sized hard drives, with various interface options and capacities up to 1TB (in some cases using two drives in one enclosure).
  • Maxtor OneTouch 4 Mini: Maxtor’s pocket-sized drives hold up to 500GB and use USB 2.0 interfaces.
  • OWC Mercury On-the-Go: These drives are available with several different combinations of USB 2.0, FireWire 400, and FireWire 800 interfaces, in capacities up to 500GB (with larger sizes expected soon). You can also buy an empty enclosure and add your own 2.5-inch drive, such as the new Western Digital Scorpio Blue 1TB drive. (The OWC Mercury cases are among the few that can accommodate the Scorpio Blue’s 12.5 mm height.)
  • Seagate FreeAgent Go: Similar to the other drives listed here, these come in capacities up to 500GB (with rumors of a 640GB model in the works) and include FireWire 800, FireWire 400, and USB 2.0 interfaces.
  • Western Digital My Passport Essential SE: This tiny drive with a big name comes in 750GB and 1TB capacities, but has only a USB 2.0 interface.

Encrypted hard drives: When you put a bootable duplicate on an external hard drive, you can’t use your backup software’s encryption feature; if the files have to be decrypted by software before the system can read them, you won’t be able to boot from that drive. And thus, ordinarily, only standard copies and versioned backups can be encrypted—though some programs you might want to use for versioned backups (think: Time Machine) don’t offer encryption as an option. This isn’t much of a worry unless, as I recommend, you store one of your backup drives off-site at all times—if someone else gets their hands on it, they have immediate access to all your data.

One way to get encrypted duplicates, or encrypted versioned backups when using a program like Time Machine, is to use a drive that features hardware encryption. Everything written to such a drive is encrypted automatically, and everything read from the drive is decrypted automatically, by circuitry in its enclosure; instead of typing in a password, you unlock the data by using a physical electronic key or smart card, swiping your finger on a built-in fingerprint reader, or entering a code on a keypad.

Several manufacturers now make such drives (or enclosures to which you can add your own drive); they come in both full-size (3.5-inch) and pocket-sized (2.5-inch) models, with a variety of interfaces. They’re more expensive than standard drives, but are an excellent investment if you store sensitive personal data. Examples include:

iPods: You can use an iPod as a backup device if it has enough free space—but remember, that will limit the amount of media you can store, and you may also wear it out prematurely, since it wasn’t meant for continuous disk use. (Only older iPods with FireWire interfaces can be used as startup disks for PowerPC-based Macs.) iPods are also more vulnerable to theft, since you’re more likely to carry them around with you—so be sure your backups are encrypted! To use your iPod as an external hard drive, open iTunes, select your iPod in the Devices list on the left, and check the Enable Disk Use checkbox. The iPod touch (and iPhone) do not support this feature without the use of a third-party hack.

Brands and warranties: You’ll usually pay more for a brand name than a generic drive. Is the extra money worth it? Often not. The drive mechanisms themselves come from relatively few manufacturers, all of which are quite reputable—it’s the cases, power supplies, and supporting electronics that vary from vendor to vendor. Look for a 3-year or better warranty, and check out the manufacturer’s Web site to look for signs of life and Mac support. But don’t be afraid of second-tier brands.

Warning: Some Western Digital My Book and Passport hard drive models can’t be used to boot a PowerPC-based Mac, even if connected via FireWire. The problem doesn’t affect Intel-based Macs. Go to Western Digital’s site for a full list of affected products.

Joe’s hardware recommendations

Don’t make decisions about hardware based on price alone. You may find the cost of a stack of DVD-R discs, for example, to be a fraction of what a hard drive costs—but that’s only part of the story. Speed, convenience, flexibility, and the ability to make bootable backups all add tremendous value to hard drives. Even if you can afford only one external hard drive, making it part of your backup system will pay for itself many times over in saved time and aggravation. If your budget permits, two or even three moderately large external hard drives are a good way to go.

Network backups are even more convenient (especially if you use a laptop with a wireless network), though they lose a few points for speed. Another advantage: if you’re sensitive to noise, having one less whirring gadget on your desk is a good thing.

If you’re looking purely for the most economical hardware path, use your built-in SuperDrive and record backups onto DVD-RW media. Your hardware cost is zero, and $50 should buy you enough blank media to last years.

Finally, don’t overlook Internet backups. If the volume of files you need to back up is reasonably small and your Internet connection is fast, Internet backup services could be a good supplement or even a substitute for conventional versioned backups. An excellent approach that gives you the best of both worlds without costing a fortune is to use a single hard drive for local duplicates and versioned backups, and then use an Internet backup service (perhaps only for your most essential files) to provide both redundancy and off-site storage for your versioned backups—without requiring you to move any hardware around.

[Joe Kissell has written many books about the Macintosh, including many popular Take Control ebooks. He’s also Senior Editor of TidBits and contributes frequently to Macworld. Take Control of Mac OS X Backups, Fourth Edition was released in September 2009 by TidBits Publishing, and it is completely up-to-date for Mac OS X 10.6 Snow Leopard.]