Information Technology Reference
Although a duplicate includes a single copy of your data, a versioned
backup has many different versions of your data—including, crucially,
copies of files that have since been deleted. This makes it much more
likely that you'll be able to retrieve the files you need in the event of a
problem. Don't get hung up on the word “version,” because even if you
never need to see a previous version of a file, you may want to see a file
that was accidentally deleted, damaged, or overwritten. And, because
versioned backups can be updated much more quickly and easily than
bootable duplicates (sometimes as often as every time you save, or as
seldom as once a day), your prospects of recovering from data loss are
much better than with duplicates alone.
You might use Time Machine to create versioned backups. It's easy to
use, and the cost is right—it's included with Mac OS X. Time Machine
isn't perfect for everyone, though, and I explain why in Decide If Time
Most people need versioned backups, even if they don't realize they
do, but in some cases they're unnecessary. If you create very little
new content on your Mac, using it mainly to surf the Web, play games,
or consume streaming content, then versioned backups won't benefit
you much. Or, if you do create lots of content but store it mostly in
the cloud—especially with services that store multiple versions of files,
such as Dropbox and Google Docs—having (local) versioned backups
may be overkill. But the more you use your Mac to create and store
unique information, the more valuable versioned backups become.
Why Create Bootable Duplicates?
Of the many things that could go wrong with your Macintosh, quite
a few of them involve problems with either the hard drive or SSD itself
(that is, physical or electronic damage) or the way data is stored on it
(directory corruption or media errors of other sorts). No matter how
scrupulous you are with saving and backing up your files, you could
find yourself, one day, facing symptoms such as these:
Your Mac crashes repeatedly, for no apparent reason.