Can a Snapshot Replace the Need for Back-ups of My Virtual Server?


Virtual servers have many benefits over traditional hardware based server farms. One benefit is the way a virtual machine takes periodic “snapshots” of your entire VM system, including applications and data.Virtual snapshots, often performed with the help of apps like vSphere on VMware machines, take place periodically, at intervals either pre-determined by the programmer or set by your IT department. Let’s take a look at how the process works.Virtualization Snapshot ProcessAt pre-determined intervals, your virtual server takes a snapshot (much like taking a screenshot of a particular screen on your computer using Ctrl + V) of your entire virtual machine disk, treating it as an individual virtual machine disk file.Since, presumably, this process will be going on while people are using the computer, the virtual machine creates a second disk file, a delta disk file, that lets user continue to access and modify files during the back-up process. This file creates a copy of the entire virtual machine when the snapshot is complete, reconciling the two in order to provide the most up-to-date snapshot.The snapshot should then be saved to the SAN, while the virtual machine is quiesced.Virtual snapshots are fast, inexpensive, and easy to complete. Previous snapshots can be deleted, saving storage space.However, there are a few drawbacks to virtual machine snapshots as a primary back-up method.Virtual Machine Snapshot Drawbacks1- When data is backed up in a snapshot, it’s impossible to write to a virtual machine disk file, although an additional VM file will accept any new write actions, making it possible to continue using applications on the virtual server while a snapshot back-up is being performed. However, read/write times may slow down due to resources being allocated for the snapshot.2 – A snapshot treats the entire virtual machine disk as a single file, making recovery of individual files or data impossible in the event of a single deleted file; the entire virtual server must be recovered as a whole3 – Applications like vSphere cannot take snapshots of virtual servers if the total CPU utilization at the time is greater than 90 % of all available resources; this could prevent snapshots from taking place during scheduled intervals4 – Snapshots may actually cause VM failure if a negative change is made to a guest OS during the snapshot process. If a virtual machine is backed up after being corrupted, you’ll want to return to a previous snapshot before the unwanted behavior occurred. Hopefully, previous snapshots have not been deleted.Snapshots: Final Analysis

A snapshot is a good “first step” back-up for a virtual machine, but make sure your company also employs other back-up methods and understands what to do in a data recovery emergency. 

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