Information Technology Reference
In-Depth Information
Sources and Destinations
The volume
from
which you back up files is known as the
source
; the
volume
to
which you back them up is known as the
destination
(or
target). Be sure to select software that can accommodate the sources
and destinations you wish to use.
All backup programs can copy data from your startup disk. Most can
also copy data from other attached hard drives and mounted network
volumes. In most cases, your destination options also include any
Finder-mountable volume. If you like, you can even back up your files
onto a
disk image
(a special file that functions as a removable disk)
,
although many programs require you to manually create the disk
image using Disk Utility and mount it in the Finder before you can use
it as a backup destination.
Finally, some backup programs can copy data directly to online storage
facilities, such as Amazon S3, an FTP server, or a proprietary
destination (Backblaze, CrashPlan Central, and the like). If you want
to store a copy of your data online, you may find it convenient to use
a single program for both local versioned backups and online backups,
if you can find one that works with all your preferred destinations.
Rolling Backups
Among those backup applications that store multiple copies of your
files, there's an important distinction to make: true versioned backups
versus
rolling backups
. In a true versioned backup, every version of
every file you designate is saved, but identical files in the same location
are never duplicated. In a rolling backup, the program creates a
complete, separate copy of all your files each time it runs—basically
a non-incremental backup. Then, after a certain number of days
or backup runs (specified by the user), the program erases the oldest
backup and adds a new one. Rolling backups give you multiple
versions of all your files, but because they copy every single file each
time they run, they take more time and require more storage space.
