Backing up one's data is as essential in computing as drinking water is essential for living. It is not a question of if you will lose data, but when.
Backing up should be done before installing any new software, and before troubleshooting system issues.
Some backups may be forbidden by software license agreements. Be sure to read these in the applications you install.
Some external hard drives may lose data upon installation of Mavericks. This may be similar to the issue which began around Mac OS X 10.3, known as the Firewire firmware bug. That issue was due to the firmware of certain drive interfaces not ready for the new operating systems. This left them invisible to the update when it began. As such backing up is good, but making sure your backup is not attached to the computer at the moment you start the installation of new software should be avoided. If uncertain how to dismount a drive, shut down your computer, and then remove the connection to it.
While viruses and spyware are not as common on the Mac platform reasons for backing up are no less important on Macs than on Windows. You might locate a file in the wrong folder, you might misname a file, you might accidently delete a file, you might find that an application is not compatible with an update, you might find that your update was not applied correctly, or you might find that you forgot some critical information about a registration code. As long as we are human, backing up is imperative for everyone who uses computers.
Those that don't back up are forced to spend thousands of dollars on data recovery, and the chances of recovery are not 100% even if one does spend that much.
The cheapest method of backing up is simply to printout information you have written down for textual data. The next cheapest to burn to CD. Followed by DVD, hard drives, flash drives, and SSDs. Note the economics here are based on initial purchase cost. Long term cost of backing up, may vary depending on the amount of data, and the format of data being stored. Some methods such as writing down music are certainly not as cheap as just recording music, since recorded music can be converted back to written music with certain software. Video and photography of course is more suited to the more expensive mediums, as much of the metadata can be lost when compressing the various formats, and the quality of what's seen is also lost. The point is, backing up should be done in the format that requires the least rework for the author of the data.
Speaking of rework, sometimes data recovery from a backup is simply a matter of locating an individual file. This can sometimes be complicated by either the fact that Spotlight hasn't indexed your backup media, or the fact that the drive in question is in the middle of a Time Machine backup. If you want to locate a file by name and are using 10.4 or later, I recommend the tool Find Any File. This will allow you to locate any file regardless of its index status on any media in 10.4 and later.
If you use a cloning software, such as described below, you can have an instant copy of the exact contents of your original, which can then be booted from
and copied back to a new drive as another clone if the original drive should fail to work. Time Machine which comes with 10.5 and later, lets you backup from a format either Apple's system discs of 10.5 or newer can recover from, or Time Machine itself can. However, that means holding on to a system that contains Time Machine on its bootable system, whether on CD or another hard disk.
If Time Machine is in the middle of backing up, you can stop it at anytime by going to Apple menu -> System preferences -> Time Machine. Do not move any files from the Time Machine drive as this may cause Time Machine to not know where it last was, but you can copy contents to another drive. Be careful, Time Machine's archiving is only as good as the amount of space it has to work with. Once it fills that, it will remove any files that don't exist on the original after a certain number of backups. For that reason I recommend manual Time Machine backups from the menubar instead of automatic ones. That same system preference will let you set up Time Machine on the menubar, and that will let you stop or start it at will, so it doesn't interfere with your production. Also Time Machine backups require there be another source to restore the backup, such as an installation disc, another clone, or Apple's internet restore option. These Macs all have Internet Restore:
iMac of an EMC of 2496; 13,x and later.
Mac Mini 5,x and later.
Macbook Air 4,x and later.
MacBook 8,x and later (no Pro no Air in the name)
Mac Pro 5,1 with EMC 2629; 6,x and later.
MacBook Pro with EMC 2555, 2563; 9,x and later.
As Macs can not run the operating system older than shipped with them be sure to at minimum have the installer disc that came with the Mac, if they are older than the Mac listed above. Time Machine will only work with Mac OS X 10.5 and later. Some older Macs will get internet restore with a firmware update:
Should you not be backed up, data recovery software titles for Mac OS X include Prosoft Data Rescue, Subrosasoft Filesalvage, and Boomerang's Boomerang. Additional ones are on this user tip. But none is as reliable as simply recovering an existing backup. And Drivesavers is an expensive but very reputable company for data recovery. Booting off CD to perform data recovery or backup from the installer CD or another hard drive may only work with these tools using the Startup Manager, instead of the 'C' key for booting.
Backups should both be off site, and off computer. Thieves can steal data if they are in the same location. Fires can damage hard drives. If a power surge should come into the computer and fry the hard drive's controller, another drive on an existing computer will basically be rendered useless.
Backing up should be the only maintenance you do, and primarily when the computer is not in use for anything else. Though intermediary backups may be useful for individual files if working on a deadline, but needing to make sure you don't lose time doing the work you do.
Archival backups can be especially useful on a project basis, to keep track of changes you make, and recovering the status of your data at a time during its production.
Both Time Machine, available in 10.5 and higher, and "Versions" available in Mac OS X 10.7 and higher and applications supporting those tools offer forms of Archival backup. As such, if you use these tools, make sure your backup destination has at least twice the capacity as your original.
Clone backups are useful if you don't need to keep track of multiple revisions, but only need to make sure the contents on your hard drive
are always restorable at the state they currently are. And they only need a destination the same size as the original. You can make an exact duplicate of your machine's software with cloning software such as Shirt Pocket Superduper, or Bombich Carbon Copy Cloner in Mac OS X, and you can do the same with Norton Ghost in Windows. Clones can save you from having to retype registration codes upon data recovery most of the time, but not always.
Even if you only backup your user data, you will be much better off than no backup at all.
So backup now. You'll be glad that you did. If you need help understanding how to use backup software to save a particular kind of data, or prepare for a possible downgrade if an upgrade fails, please ask first, and someone in the forums can help you.
See Apple's articles on backing up as well: