Information Technology Reference
Multi-computer backups: Time Machine is fine for backing up,
say, two or three Macs to a single drive. But the more Macs you back
up, the less sense Time Machine makes, because it wastes space
with duplicate files and bogs down the host Mac (or Time Capsule).
NAS and AirPort Disk backups: Time Machine doesn't work
with many network-attached storage (NAS) devices as your backup
destination. (A NAS is essentially a hard drive with a network
interface, which functions as a stand-alone file server without an
attached computer.) Apple's Time Capsule is a notable exception,
and there are several others—but not all NAS devices work with
Time Machine. And although it's possible to get Time Machine
to recognize an external disk attached to an AirPort Extreme Base
Station, Apple doesn't support this arrangement and problems are
likely to occur.
So, to back up multiple computers without a Time Capsule or
supported NAS, you must either physically shuttle a drive from
one Mac to another or keep it attached to a Mac that will share
the drive over your network using File Sharing. If neither solution
is practical for you, or if you've already invested a lot of money
in other network-based storage for backups, Time Machine won't
meet your needs.
Backups of Boot Camp and network volumes: Time Machine
can back up your startup volume and most other mounted local
volumes (such as a second internal hard disk or a secondary
partition of your main disk). But to back up Boot Camp partitions
or mounted network servers, you'll need a different program.
Fine-grained control: Time Machine offers simplicity at the
expense of flexibility. What if you want to exclude from your backup
all files that match a certain pattern (disk images, videos, music)?
You'd have to add each item individually, or the folders that contain
them, to Time Machine's Exclude These Items from Backups list
a different scheme for deleting old backups? Or you want to store
some kinds of files in one destination, and other files in another