Tag Archives: back-up

How good are your backups?

PICT0008We 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?

Sometimes the best way to recover Windows data is Linux

knoppixMy Windows laptop refused to boot into Windows. The ominous error message was:

Windows could not start because the following file is missing or corrupt:

\windows\system32\config\system

A quick Google suggested that the registry had been corrupted. I tried various things to recover the OS, including using the XP recovery console to manually restore a backup of the registry. It didn’t work.

No problem. I have a fairly paranoid back-up regime. All the important information on my laptop is also stored on my subversion server. I could just reformat the laptop, reinstall the applications (including subversion) and check out all the files again. Except that I hadn’t thought to include my wife’s files on the laptop in my back-up plans. Oops. After hours of making no progress recovering the data. I tried Knoppix. I got access to the data in not much longer than it took to download Knoppix.

Knoppix is a Linux distribution that can run from a CD (i.e. it doesn’t require installation on your harddisk). It is also capable of understanding Windows file systems. To use it:

  1. Download the latest Knoppix CD .iso file (approx 700MB). Note – The DVD version is much larger.
  2. Burn the .iso to a CD, for example using the free Active ISO Burner.
  3. Boot the stricken machine from the Knoppix CD. You may need to change your system to BIOS to boot from the CD first. How you access the BIOS varies between machines. On my Toshiba laptop you press F2 as the system boots.
  4. Drag and drop data from the stricken machine to a USB harddisk or memory stick. Or copy to another machine using FTP from Knoppix. The Knoppix user interface is easy enough to use, even if you haven’t used Linux before.

Note that you don’t have to enter your Windows password to recover the files. This brings homw how easy it is to get data off a password protected Windows machine, if you have physical access to the machine. Another good reason to encrypt sensitive data on your laptop, for example using the free Truecrypt.

Thanks Knoppix! I’ve added you to my mental list of worthy software causes to make a small donation to one day. Obviously you need access to a functioning machine to do the above. So why not make a Knoppix CD now, while everything is fine? You never know when you might need it.

Further reading:

Life hacker: Rescue files with a boot CD