Which leads me to understanding why this can work as a backup strategy. Instead its instead folding that snapshot into its ancestor (back to the vdi or another diff file). Restoring to the snapshot point is as simple as throwing away the snapshot-file – the commit log – and unfreezing the snapshots ancestor.ĭeleting a snapshot is not removing all the changes in that commit log. Its a diff of stuff thats changed since the snapshot took place. This file is in essence a kind-of commit log against the underlying virtual file system of everything that has happened after the snapshot in time. Instead, all writes go into the file associated with new snapshot. When you take a snapshot of a virtual machine, in the default “normal” mode, the associated parent (either the virtual machine image or another snapshot) is frozen and no longer written to. A snapshot turns out to be the diffing system I was looking for. How snapshots actually work makes it extremely powerful for backups. You can also do crazy things like go back to a snapshot and create a branch from that snapshot – taking your virtual machine in multiple experimental directions from a single restore point.
You can restore your virtual machine to any snapshot in the history. In the simplest use-case you have a linear progression in time of various snapshots. The best part is I can take a snapshot of a system even while its running. If I create a snapshot, I can go back to that point in time. The canonical solution turns out to involve a VirtualBox feature known as snapshots which I had before now known nothing about.įrom a users perspective, a snapshot is a restore point. Everytime I launched my virtual machine Id have to wait for this boring 5-10 minute process. Moreover committing such a large file is tediously slow. This solution wasnt very space efficient. vdi file, the repository had grown to 40 GB+. Unfortunately even its diffing ability in this situation was lacking. I found and tried Boar, a versioning system which attempts to work well for binary files. Git turns out to have a sensible maximum file limit, which was a pretty big “hey idiot… what are you doing” warning.
Then Id point CrashPlan at the associated repository which would be backed up in the background. One thought I had was that before launching the virtual machine in a batch file or script Id commit the vdi it to a version control system. I really wanted some kind of diff-based approach to backing up the large file. I tried all kinds of hair-brained schemes to backup my virtualbox image in something resembling automatic. How can I have any guarantee that that image is in any kind of consistent state? Backing up with a versioning system This is, of course, problematic as CrashPlan is most likely running its backup while Im actively working in my virtual machine. However, the dumb me was just pointing CrashPlan at the directory with my virtual machine images and hoping for the best. Here at work we use CrashPlan which seems to do a decent enough job automatically backing up the directories I tell it to. The most important thing I want to backup is my Ubuntu VirtualBox image. I needed to make sure my backup strategy was solid.
This is the second time in a month this has happened. And now to the fun subject of virtual machine images!
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