How to test your backups against medium degeneration?

Because most storage media degenerate over time (CD, DVD, harddisk, tape), it is very important to test your backups. Is there a way to monitor the condition of your backups?

I am looking for both hardware and software solutions, as well as strategies you can use. For example:

• Hardware solution: using the S.M.A.R.T. features of harddisks; ...
• Software solution: using a backup tool that calculates MD5 checksums; using a tool for checking the Reed-Solomon ECC on CDs; ...
• Sample strategies: keeping multiple copies of your backup and doing a file comparison every month; scanning every now and then the MD5 checksums calculated by your backup tool; ...

The only way you can be sure of your backups is to restore them. Checksums may verify the content of your medium but they won't tell you if a restore is possible: what if you're not backing up everything you need to?

The complexity of this depends on whether you're backing up for bare-metal recovery (which has its own issues) or just carrying out data backups.

For data backups, one option is to build a virtual machine and periodically fire it up and test a restore. This is less than valid for bare-metal because the VM will undoubtedly require a completely different set of e.g. drivers, etc. I guess (depending on your OS and tool-set), if you were really keen, you could probably script the process of carrying out the restore and do it for every backup.

You should be verifying your backups before storage to begin with. A lot of attention is brought to how hard it is to do backups, but no one ever thinks to check them before safely bringing them off site.

I generally only wait for 1 bad write to a CD-R to toss it, for how cheap they are, and focus on S.M.A.R.T. results for HDD media to tell me when to replace them.

Best of luck to you.

With today's large amounts of data and relatively small optical disc sizes, backup to removable HDD's seems best to me. Also, HDD's are easier to maintain both physically and in terms of filling data onto them.

I regularly run GRC's SpinRite on my disks. SpinRite tests the written data, and optionally refreshes or even recovers it.

testing your backups is an interesting point. however, it is time consuming and questionable in my opinion. because if a medium is damaged, your backup may be a total and partial loss, thus testing is rather moot.

i prefer multiple backups. as for optical media (not my preferred choice), if you create a new copy every, say, 5 years you should be on the safe side, if you have two copies (kept in different locations to reduce the risk of data loss in case the house burns down :), the chance that at least one has survived the aging process is very high. of course the risk is decreasing reciprocally to the number of backup sets.