Ask an Expert What is the recommended amount of snapshot space I should reserve for my VM's?

Answer:

It really depends on how much you are going to use them.

A snapshot can never grow larger the original disk.

The big factor will be how many snapshots and how long are you going to keep them.

You also need to factor additional space if you snapshot a VM's memory as well, this will be as large as the RAM assigned to the VM.

I leave about 50GB of disk space for my snapshots (for all VMs), I do not use them that often though.

These are the files that make up a snapshot.

*–delta.vmdk file - This is the differential file created when you take a snapshot of a VM (also known as REDO log). When you snapshot a VM it stops writing to the base vmdk and starts writing changes to the snapshot delta file. The snapshot delta will initially be small and then start growing as changes are made to the base vmdk file, The delta file is a bitmap of the changes to the base vmdk thus is can never grow larger than the base vmdk. A delta file will be created for each snapshot that you create for a VM. These files are automatically deleted when the snapshot is deleted or reverted in snapshot manager.

*.vmsd file – This file is used to store metadata and information about snapshots. This file is in text format and will contain information such as the snapshot display name, uid, disk file name, etc. It is initially a 0 byte file until you create your first snapshot of a VM and from that point it will populate the file and continue to update it whenever new snapshots are taken. This file does not cleanup completely after snapshots are taken. Once you delete a snapshot it will still leave the fields in the file for each snapshot and just increment the uid and set the name to “Consolidate Helper” presumably to be used with Consolidated Backups.

*.vmsn file - This is the snapshot state file, which stores the exact running state of a virtual machine at the time you take that snapshot. This file will either be small or large depending on if you select to preserve the VM’s memory as part of the snapshot. If you do choose to preserve the VM’s memory then this file will be a view megabytes larger then the maximum RAM memory allocated to the VM. This file is similar to the vmss (Suspend) file. A vmsn file will be created for each snapshot taken on the VM, these files are automatically deleted when the snapshot is removed.

The answer is provided by Eric Siebert [vmware-land].