and Preservation: How do I ensure Data Integrity of Backups?
and recovery management software is not a magic wand that you
wave to grant you eternal and automatic continuity in case of
data loss. One crucial element of any backup software is the
verification or validation of two important stumbling blocks
- the backup archive and the medium of storage. This article
reveals the secrets of why validation is of crucial importance
whether you are a home user or a business owner and suggests
ways to ensure that your data remains 'restore-able'.
Regular and consistent backup is the only
preventive measure that allows you to resume where you left
off when disaster strikes. The main issue here is, however,
being able to restore all your lost data to its original
state with 100% accuracy.
A recent article in CIO magazine states "storing
data is the easy part, recovering data is another story".
If your software does not guarantee 100% restores and
does not have a level of validation that guarantees the integrity
of the data, then replace it.
By integrity I mean consistency, accuracy, and
correctness of the data.
Your software must ensure also ensure data
preservation, i.e., it must have mechanisms to ensure the
that the medium to you which you are backing up can preserve
your data over a long period of time (at least until your
Types of Storage Media
Backing up to the same drive as the native data is useless -
how can you ensure that you are preserving your data when a
hard disk crash can mean losing everything. In essence, don't
put all your eggs in one basket.
Backing up to another hard drive is an option
many are choosing. Tapes have a longer life than most media
but in a home-user environment this is impractical and expensive.
Many home-users are now backing up their data to CDs and DVDs
(which have a greater storage capacity), to USB pen drives and
similar media. If your backup software does not provide the
possibility of storing to a variety of media (at least another
hard disk, USB drive or CD/DVD) then get rid of the product
immediately. You are at risk.
What's Validation and Preservation?
Simply, put validation or verification is the ability to check
the integrity of your backup archive. The backup archive
is the single file in which your backup software stores the
original data. Validation allows you to make sure that the data
in your backup archive can be reproduced easily and with 100%
accuracy. The integrity of the backup archive, however,
does not completely depend upon the software but also on the
type of medium chosen and its long term shelf-life.
Validation ensures that the type of medium you have chosen (e.g.
a CD, DVD, USB or Tape) has not been compromised and
that your original data may be restored with 100% accuracy.
This means that your data is preserved.
Backup Software and Validation
As explained earlier, the main aim of a backup solution is that
the data that has been stored in an archive is the exact replica
of the original data. This is what ensures you that you can
continue where you left off when you lose your data.
According to an article in CIO Magazine, a
survey carried out reported 59% of SMB backing their data with
only 32% testing their restore processes at least once a month.
One can only imagine that the number of home-users
testing their restore processes is much, much less. Instead
they would probably burn their data in native format on a number
of CDs or DVDs - but this is extremely counterproductive as
the amount of data we store grows daily and therefore we need
more storage media. DVDs might not be expensive but if you need
3 or 4 a week, then you will either spend a fortune in backup
or backup less frequently.
The problem of storage aside (read How
do I maximise storage capacity for backup?), you should
not only focus on backup but also on the integrity
of the data that has been backed up to ensure 100% accurate
reproduction of the data. This is where validation comes in:
with advanced levels of validation such as bit-level validation,
the backup software itself tests the integrity of the data down
to bit level by reproducing a test restore right after each
backup is performed. This may see backup taking longer but it
guarantees 100% restorability of the data in question.
Lower but satisfactory levels of validation
include Cyclical Redundancy Checks (CRC) which cannot
guarantee 100% accuracy as bit-level validation does. CRC encodes
a checksum (a value used to ensure data are stored or transmitted
without error) with the data that is going to be backed up.
The CRC then performs a 'dummy' restore and calculates a new
checksum of this data. If the new checksum is identical to the
one encoded, then your backed up data is error free.
Ideally, your backup software includes both
and other varying levels of validation to allow users discriminate
between more and less important data with the latter being awarded
minimum or no validation in the interest of speed.
Also, your backup software should perform
certain tests to make sure that your data is preserved for future
Tests should also include you performing regular
(e.g., once every couple of months unless you have very
important data such as photos, study-related papers, financial
documents, emails) test restores to ensure 100% accuracy.
This need arises because no backup software
can guarantee the integrity of the media used - a faulty
hard-drive may reproduce corrupt backup archives no matter how
good the backup software is.
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