A virtual machine snapshot is a function of VMware that allows you to create a point in time image of your server that you may revert to in the future. When a snapshot is created a delta file is made for each hard disk attached to the virtual machine. This means that if you roll back a snapshot, all hard disk changes made subsequent to the snapshot are lost.  

Note: Most server owners find this restriction to be quite prohibitive, because changes made to production data are lost if the snapshot is rolled back.

How long are snapshots retained?  Due to this restriction, as well as concerns of disk growth and potential corruption, snapshots are retained for no more than 72 hours.

Appropriate Uses for Snapshots

• Preserve an image just before a major upgrade as protection from a failed software installation.
• Testing and experimentation with large changes, where the upgrade could potentially damage user data.

Inappropriate Users for Snapshots:

• Preserving an image to retain a previous version of software, but then allowing users to make changes to production data.
  • Production changes would be lost if rolled back.
• Making a snapshot of a system for use in deploying clones of the system in the future.
  • Because there is a great deal of host-specific customization for each server, systems are not installed from clones.

Note: A shutdown of the server will be scheduled so the snapshot can be made while the software is in a known state. If you expect to need the snapshot made or rolled back outside of normal business hours, it is especially important to coordinate with the systems support group in advance.

To schedule a snapshot: send a request to systems-support@cornell.edu at least 48 hours in advance so we can make arrangements for a staff member to be available. We suggest using the standard maintenance windows as described on the Scheduling Maintenance page.