We all know we need to do backups. But that is only half the story. Have you actually checked you can read them back if you need to? I have heard stories of people religiously backing up to mag tape every day for years, only to find out the tapes were corrupt and couldn’t be read back when needed.
I checked my backups recently to ensure I could read them back. Here is what I found out:
- I was backing up my SVN repository on my Mac Mini to a single .tar.gz file which I then copied across onto a USB disk attached to a Windows box. The file had grown unnoticed to >4GB in size. But the USB disk was in FAT format, which has a maximum file size of 4GB. The the file was quietly being truncated to 4GB and I couldn’t uncompress the file when I tried with gunzip.
- I was backing up from my Windows box to DVDs in ‘live’ format. These were not readable by my Mac mini, which would have been a problem if neither of my Windows boxes were working. I have now changed to ‘mastered’ format, which is readable by Windows and Mac.
- I was backing up the .mdf file my OnTime bug tracking database. It turns out you can’t just swap one .mdf file for another and re-start OnTime, as you get an internal consistency error. I am now creating and backing up .bak files, which you can restore.
I have lots of redundancy in my backups – backing up in multiple formats (files, SVN repository and Acronis disk images) to multiple media (multiple machines, USB disks, DVD and online). So none of the above would have spelt disaster. But it does bring home the importance of testing your backups from time to time and of having multiple forms of backup. If you think backing up to a single USB disk is enough you should read this. If you are relying purely on an third party online backup service you should consider what would happen if they went bankrupt – not inconceivable in the current economic climate.
Are you relying on a single backup strategy? When was the last time you tested your backups?