Snapshot deletion

[DavidDeb]

Hello all,

I have a n00b query, for which I have found no direct answer.

When deleting a snapshot, the 'difference' will be passed to the base .VDI (in the case of dynamic differencing HDs, which I believe to have read). I would like to know - as a 'Rule-of-Thumb' - what percentage or portion of the snapshot size will be passed back to its base HD. I assume here that the file size includes a certain 'Management Overhead' and is not 'pure' difference.

The point is that I am going to clean up on a particular virtual machine and would like to know if my combined difference image data will cause the base HD (.VDI) to be overfilled.

Thanks in advance for any pointers on this issue.


DavidDeb

[socratis]

The point is that I am going to clean up on a particular virtual machine and would like to know if my combined difference image data will cause the base HD (.VDI) to be overfilled.

I'm not sure what exactly you mean by "overfilled". If you're talking about the free size as seen in your guest, that will be the same as the free space you had in your snapshot. If you're talking about the size that the VDI occupies on your host, then that will never exceed the maximum size that you have set for your VDI.

[mpack]

I would like to know - as a 'Rule-of-Thumb' - what percentage or portion of the snapshot size will be passed back to its base HD. I assume here that the file size includes a certain 'Management Overhead' and is not 'pure' difference.

I think you have a misunderstanding of what snapshots do. They do not increase the capacity of a disk, they just provide alternative contents for some parts of the existing capacity. When a snapshot is merged with a following state then the ability to revert to the state represented by the snapshot is lost.