We all know that we should regularly back up our data. And we also know that Apple has made it easy to do so with the Time Machine technology that’s been built into OS X since Leopard (in the Applications folder). Yet the majority of us still don’t regularly back up our Macs.

While some may fail to do so because they believe it’s a complicated process, and others because of their misplaced faith in the robustness of hard drives, many Mac users simply don’t know what to back up and how to best go about it. We’re here to help.

Decide what to back up

Perhaps the best way to determine which data you should back up is to consider just how terrible you’d feel after losing a particular class of data.

The personal and irreplaceable When considering what to back up, this is the first broad filter you should employ – data and media that hold a special place in your heart and can’t be recreated. High on the list of the personal and irreplaceable are photos and home videos. Although it’s possible that you have the original images and videos on a tape or storage card, unless you’re the worst sort of hoarder, it’s unlikely.

Data critical to your work Nearly as important as the personal and irreplaceable is data that, if missing, threatens your job or freedom. Such files include work that you’ve brought home from the office, documents you’ve spent months creating, the next great screenplay, and tax records.

Data that’s a pain to replace A surprising amount of the stuff on your hard drive falls into this category. This includes music in your iTunes library (music you’ve ripped from CD or purchased online), iTunes videos, your browser bookmarks, address book contacts, and calendar events. (Of course, if your business depends on those bookmarks, contacts and events this class of data moves up in the order of importance.)

All the rest This can be old email, PowerPC applications that you haven’t run since upgrading to Mac OS X Lion, your CV from 1997 – just about anything that you thought you might need but, in truth, were unlikely to ever look at again.

Know your backup options

The days of casually jamming a floppy disk into a slot and dragging a couple of files onto it are gone forever. We now have multiple gigabytes of data to back up. Here are a few of your options.

Writable optical media Although Apple sees writable CD and DVD media as something of a dead end, a lot of today’s Macs still have a SuperDrive. Regrettably, writable CDs and DVDs can degrade over time, particularly when exposed to sunlight and moisture. Also, scratch one badly enough and your data is toast. Saving to CDs or DVDs is a terribly slow means for backing up a lot of data. But in a pinch, it’s a reasonable solution, where you can easily move data from one computer to another without using a network.

Time Machine doesn’t let you choose what to back up. Instead, you exclude the items you don’t want backed up. Doing so is a good way to save space

A second hard drive Many people opt to attach a second hard drive to their Mac to use with Time Machine. Just plug in a FireWire or USB drive (or add a second internal drive if your Mac allows), switch on Time Machine, select the drive as your backup disk in Time Machine’s settings, and let the software do its stuff. This may be the easiest way to back up your data, as it requires no more effort than purchasing and plugging in a compatible hard drive.

Although Time Machine doesn’t allow you to choose specific items to back up, it does let you exclude items to save space.

Configuring a Time Machine backup with a second hard drive is simple. The greatest effort it takes is purchasing the drive and plugging it in. But using an external drive won’t protect you from a cataclysmic event – a massive power surge, fire or flood. You could lose both your Mac’s hard drive and the secondary drive attached to it.

Two external hard drives What would you need two drives for? The answer is extra peace of mind. Rotate the drives and keep one off-site – in a safe deposit box, at work, or at a friend’s house. (If you must store it on-site, get a media safe that’s waterproof and fireproof.)

Your backup schedule might look like this: attach Drive A on Monday and let it back up your Mac throughout the week. Detach it on Sunday to bring it to the office for safe-keeping. Swap in Drive B, allowing it to back up the Mac during the next week. At most you could lose a week’s worth of work.

Time Capsule If you have multiple Macs to back up, check out Apple’s Time Capsule wireless hard drive and router (2TB £249; 3TB £399). Like using a single hard drive, using a Time Capsule means that your backup drive is on-site.

Online backup Online backup provides extra protection from on-site disasters. Using an online backup service such as Apple’s own iDisk (while it still exists) or iCloud, Dropbox (www.dropbox.com), or one of the many other commercial online backup services such as CrashPlan (www.crashplan.com) you can upload your most precious data to ‘the cloud’.

Make your backup plan

Once you’ve determined which data is the most important to you, consider the steps you should take to back it up.

For your most prized data, you must have a redundant backup plan. This starts with at least one local backup drive running Time Machine. Then consider a second backup drive that you keep off-site and rotate in on a regular basis.

For the crème de la crème of your data collection – your iPhoto library and iMovie projects, for example – add an online storage service. This provides off-site backup without your having to leave the house. If you can get by with just a couple of gigabytes of storage, Dropbox is an excellent and free choice. If you have a lot of data (and plenty of time to wait for it to upload), consider a more flexible online storage service such as the £33 per year CrashPlan+ (www.crashplan.com).

Backup boosts

Still feeling nervous about all your data? Here are some more measures to consider depending on your situation.

A bootable backup If you need to get up and running fast after a hard drive disaster, you might want to add a bootable copy of your data to your plan. This is an exact copy of your startup drive that you create on another hard disk – one from which you can boot your Mac just as you can from your startup drive. Use a tool such as Shirt Pocket’s $27.95 (£13) SuperDuper (www.shirt-pocket.com) or Bombich Software’s free Carbon Copy Cloner (www.bombich.com).

Hourly protection If you have a hot project you’re working on, consider jamming a USB key drive into a spare slot on your Mac and copying that project’s files to it every hour or so. You can create an Automator workflow to automate this process (see macworld.com/6868).

Safekeeping for serial numbers While you don’t need to back up your programs – because you can always install fresh copies – you should keep a record of your applications’ serial numbers and registration codes. Similarly, having a copy of your passwords and internet configuration information will be a godsend if your hard drive dies. You can back up many internet passwords by making a copy of your keychains. You’ll find them in youruserfolder/Library/Keychains.

Agile Web Solutions’ $49.99 (£33) 1Password (www.agilebits.com) is a terrific way to create and store passwords. Additionally, you can export 1Password archives for backup. As for internet configuration settings, one of the easiest ways to back them up is to take screenshots of the appropriate Network system preference and AirPort Utility screens and then print and back up those screenshots.

See also: How do I restore my Mac using Time Machine?