Space requirement in datastore to delete snapshot(s)

In this post, I will explain the snapshot deletion process in VMWare 4.0 and VI infrastructure 3.

Suppose we have 3 snapshots of 10, 30 and 20 GB respectively. When you click on delete snapshot, following happens:

-> A snapshot helper is created which holds all the changes.

-> Snapshot 3 will be copied to snapshot 2 and snapshot 2 might grow upto 50 GB

-> Snapshot 2 will be copied to snapshot 1 and will grow till 60 GB

-> Snapshot 1 will be committed to the original VM Disk file (flat.vmdk)

-> Helper snapshot disk will be committed to the original disk.

-> All snapshots will be deleted.

Snapshot deletion procedure:

Please note, when snapshots are created, original vmdk file becomes 'read-only' and all the changes made after are written to separate 'delta' disks.

This process changed in later version on VSphere 4.1 (and above), each snapshot gets merged to parent disk individually i.e. extra free space is not required - except for the helper file.

Also, below are some points to be noted about snapshots:

1. A snapshot file cannot grow larger than its parent disk.

2. Disk files are not deleted until all the snapshots are committed to parent disk.