The Joys of Xen Snapshots

One of the Windows VM's that I have is for hardware drivers.  I don't like installing custom drivers because they never see to go away.  This is where the snapshot feature of qcow2 comes in handy.  I just take a snapshot before installing the drivers.  If the hardware doesn't work out, I just apply the old snapshot and no more messy drivers!

This also works well when trying out new software.  Lots of software comes with adware.  Adware is sometimes hard to remove.  By making periodic snapshots, you can rollback the adware, instead of trying some poorly written anti-virus program.

mycomputer disks # qemu-img snapshot -l vm1.img 

Snapshot list:

ID        TAG                 VM SIZE                DATE       VM CLOCK

1         fresh_install             0 2012-08-21 19:06:12   00:00:00.000

mycomputer disks # 

The qemu-img command allows you to create, apply and delete snapshots.  As mentioned in a previous post, it is highly advised to shutdown your vm before taking/applying a snapshot.  The -c option is used to create a snapshot.  The -a option is used to apply a snapshot.  The -d option is used to delete a snapshot.  

More and more filesystems are starting to support copy-on-write features.