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Backup Software
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data. One company I worked for had
so much data it took more than a
day to back up all of the machines.
Thus, full backups were done over
the weekend, with incrementals in
between. Also, in a business environment
with dozens of machines,
trying to figure out exactly where the
specific version of the data resides
increases the recovery time considerably.
Finally, you must also consider the
cost. Although you might be tempted
to get a larger single drive because
it is less expensive than two drives
that are only half as big, being able to
switch between two drives (or more)
adds an extra level of safety if one
fails. Furthermore, you could potentially
take one home every night. If
you are writing to tape, an extra tape
drive also increases safety; it can also
speed up backups and recovery.
Which Tape?
Some companies remove all of the
tapes after the backup is completed
and store them in a fireproof safe or
somewhere off-site. This means that
when doing incremental backups,
the most recent copy of a specific
file might be on any one of a dozen
tapes. Naturally, the question becomes,
“Which tape?” (see also the
“Whose Data” box). To solve this
problem, the backup software must
be able keep track of which version of
Incremental vs. Differential
Because of the amount of data, businesses
frequently have a two-tiered backup scheme.
Once a week, a full backup is done (of every
single file); on subsequent days, backups are
done of only those files that have changed.
This approach is referred to as an incremental
backup. Although it saves media, it
potentially takes more time to recover. With
this method, you first need to restore the
full backup and, depending on which files
have changed, you might need to access
every single incremental backup.
One alternative is a differential backup,
which stores only files that have been
changed since the last full backup. This has
the advantage of saving time compared with
an incremental backup, because you need to
restore from, at most, two backups.
Backup Alternatives
If you are running Linux and your software repositories are configured properly, a number of
backup applications are available through your respective installation tool (e.g., YaST, Synaptic).
In fact, I found more than two dozen products that have defined themselves in one way or another
as a backup tool (not counting those explicitly for backing up databases).
Here are a few important questions to ask about your backup software:
n Is your hardware supported?
n How does the software deal with database backups?
n Can you do a directed recovery (i.e., to a different directory)?
n Can the software verify the data after a backup and restore?
n Can the software write to multiple volumes?
n Do you really need all of the features?
n Can the software do a backup of a remote system?
How is the backup information
stored? Does the backup software
have its own internal format or does
it use a database such as my SQL?
The more systems you back up, the
more you need a product that indexes
which files are saved and where they
are saved as well. Unless you are
simply doing a complete backup every
night to one destination for one
machine (i.e., one tape or remote diwhich
file is stored where (i.e., which
tape or disk).
Once a software product has reached
this level, it will typically also be
able to manage multiple versions of
a given file. Sometimes you will need
to make monthly or even yearly backups,
which are then stored for longer
periods of time. (This setup is common
when you have sensitive data
like credit card or bank information.)
To prevent the software from overwriting
tapes that it shouldn’t, you
should be able to define a “recycle
time” that specifies the minimum
amount of time before the media can
be reused.
Because not all backups are the same
and not all companies are the same,
you should consider the ability of
the software to be configured to your
needs. If you have enough time and
space, software that can only do a
full backup might be sufficient. On
the other hand, you might want to be
able to pick and choose just specific
directories, even when doing a “full”
backup.
Support
One consideration that is often overlooked
is the amount of support available for your
product. Commercial support might be necessary
if implementing the backup solution
for a company. However, the amount of free
support (forums, mailing lists) can be an issue.
When considering open source software
of any kind for a business, I always suggest
taking a good look at the product’s website.
If the product has not been updated in three
years, you might want to look elsewhere. If
forums have few posts and most are unanswered,
you likely won’t get your questions
answered either.
Many of the products I looked at have
the ability to define “profiles” (or
use a similar term). For example, you
define a Linux MySQL profile, assign
it to a subset of your machines, and
the backup software automatically
knows which directories to include
and which to ignore. The Apache profile,
for example, has a different set
of directories. This might also include
a pre-command that is run immediately
before the backup, then a postcommand
that is run immediately
afterward.
Storage
Whose Data?
One important aspect is the ability to write
data from different sources to specific
media. For example, where I work, each
customer is assigned specific tapes (often
referred to as a “pool”). With the use of
labels written to the tape, the software can
tell which tape belongs to which pool, so
that data from different environments is
not mixed. This scheme is very useful if, for
example, one customer wants weekly backups
stored off-site and another customer
frequently requests the backup tapes to load
them into a local test system.
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