Verification and Preservation: How do I ensure Data Integrity of Backups?

Backup 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 next backup).

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 use.

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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