Attaching Difference Files, planned

[ProfMac]

I am short on disk space, and I am exploring VirtualBox.

I constructed a Ubuntu 10.02 Guest, lifepod, on a Windows XP host. I installed SAMBA on lifepod, and ran NT backup on a second XP machine, laptop, depositing the *.bak files into the lifepod appliance.

Each time I backed up a laptop partition, I gracefully shut down lifepod and took a snapshot. I have a sequence of files with UUID style names in the snapshots directory. My presumption is that each snapshot file holds the contents of that particular partition-n.bak file.

I am testing the restore function on another virtual machine, beachhead. Beachhead started as an empty machine with a Windows XP CD and the dos floppy image of the nt backup sif files. I successfully installed windows, and the system state, including user accounts. This involves a call to Microsoft to reactivate the operating system. My goal is to prove that my backup works.

During the restore of the partitions, the Host hard disk is expected to fill up. In fact, I have beachhead on pause at this time, with a full disk imminent.

( This is actually a simplification. When I started, I had maybe 30-50 GB more free space than two copies of the laptop file system should need, but somehow dozen's of GB seem to be missing. I haven't chased that down, can't make a convincing report , and am mostly ignoring it for now. I did run a XP search for all file and sorted them by length, but did not get any insight. I did a chkdsk reboot of Host with nothing interesting to report. )

I created SecondaryLifepod. This is an export/import appliance made from Lifepod when the backup disk was detached. It complains that /srv/samba/share/laptop is missing when it tries to boot, when no difference disk is attached. This is expected. I have tried attaching various disk images, choosing various particular difference images from the Lifepod/snapshots directory. When I start the SecondaryLifepod, a new small difference image is created under the image I think I selected. This seems rational.

The next planned steps are to verify that, as I walk back in time up the chain, fewer and fewer backup files are in SecondaryLifepod/srv/samba/share/laptop{version}

Upon verifying that, I plan to trim the difference chain walking backwards, to recover enough disk space to do the next partition of my restore.

Sadly, each time I attach a difference disk, all of the backups appear to be in the directory. I have paused a bit to report and think.

I am using the new release 4.1.18r78361

[mpack]

Snapshots are not backups, quite the contrary - they decrease redundancy and increase risk of data loss.

Your concept (which I think I detect) that snapshots are containers which contain changed files - is quite wrong. VirtualBox knows nothing about files. Snapshots contain changed disk sectors. It will generally be impossible to recover complete files from a lone snapshot, since even if the entire file is present, the filesystem will not be. Individual files and the filesystem hooks needed to manage them will tend to be scattered across the snapshot chain - hence all snapshots need to be present in a single folder to recover anything.

[ProfMac]

Yes, I did think of snapshots in terms of disk sectors as I planned this out.

I want to take 1 disk to an earlier point in time, before I added a large file. I have a snapshot before, and after.

I want to attach this earlier time point in a different vm.

How can I do this working from the existing snapshot directory?