Snapshots and the effect on VM Performance

All Cloud Enterprise, Cloud Dedicated and Cloud Private customers are able to create Snapshots, which preserves the data and the state of a Virtual Machine at a specific time. Obviously these are immensely important for production and test environments that require zero or as little down time as possible. Snapshots will allow you to save the state of the VM prior to an update, so in the event the update causes harm to the server, the Snapshot will allow you to recover the VM back to the state prior to the install.

Snapshots Are Not Meant For Backups

Snapshots are not and should never be used for a replaced for backups. Hosting.com provides backups, both standard and advanced, and we recommend that you take avantage of this, rather than attempting to use snapshots as backups. For more information regarding our backups, please refer to the following;

http://www.hosting.com/services/managed-services/data-storage--protection/managed-backups

Snapshot Creation And Impact

However a Snapshot can also impact the I/O performance of a VM as well. When a Snapshot is created, it generates a file, called the delta.vmdk, which is basically a mapping of  all the changes that have happened to the VM or the VMDK. So everytime a Snapshot is created, a delta file is created. So now when you introduce a Snapshot you introduce an additional resource. What now happens is that any new data written to the VM is now read from both the original VM (VMDK file) and written to the new VM (Delta.VMDK). This puts additional stress or overhead onto your server, which now will affect your I/O performance.

Hosting.com recommends that you only create snapshots in the event that you are making changes to your server and you are unsure of the change and the impact to your server. However once the changes have been made and you verify there are no problems with the recent changes, we recommend that you remove the snapshot. We understand that at times you may want to hold on to your snapshots, however at the same time we don't want you to lost any performance by doing this, so we have a 7 day policy on saving snapshots.  Since a snapshot is time-stamped on creation, we can safely go through and remove any snapshots that have been stored on the VM longer than 7 days. There are no exceptions to this, unless you are a Dedicated customer and have your own ESX/ESXi cluster, then any policies you have in place would apply.

Snapshot Recommendations

While not recommended directly from VMware, it is recommended that snapshots stay in place no longer than 48 hours. Also keep in mind that the larger a snapshot is, the longer it takes for theVM to commit to restoring that snapshot. Larger snapshots can take anywhere from a couple of hours to a day.