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Snapshot, Backup or Replication

Paragon Software Group | May 6, 2016
We find out the differences between basic data management techniques, such as snapshot, backup and replication.

This vendor-written piece has been edited by Executive Networks Media to eliminate product promotion, but readers should note it will likely favour the submitter's approach.

Today, it's hard to imagine corporate IT without virtualization. Virtual environments have great potential in private or semi-professional circles as well, and have also become a point of interest for small businesses since Microsoft's release of its proprietary hypervisor, Hyper-V, for free. As a result, Hyper-V is making tremendous gains in the industry. Alternatively, VMware is clearly the market leader with its ESX / vSphere solutions. But what is the best way to back up a virtual Hyper-V or ESX server? What different approaches are there and where are the benefits and drawbacks? We have noticed uncertainty about this topic when talking to customers: "Why do I need an extra backup solution? Our virtualization solution already offers native snapshot creation".

It's just that creating snapshots is not suitable for reliably backing up data and systems which significantly contribute to truly sustainable business operations. This requires a bit of an explanation; as such, this article primarily relates to backing up VMware-based systems, but the approaches described are largely universal.

Snapshots are not backups!
It's a widespread misconception that a snapshot of machine can substitute or be used as a backup. While snapshots and backups do have a few things in common, their intended purpose differs drastically. 

A few facts about snapshots:

  • A snapshot is a recording of the state of a virtual machine at a particular point in time.
  • A snapshot is not a full copy of a virtual hard drive, but a delta file or »change log«.
  • The current state of the virtual machine is a combination of the original virtual disk and snapshots.
  • ESX / vSphere snapshots are saved in the immediate vicinity of the original virtual data media.
  • VMware snapshots are always »thin-provisioned« and thus have a detrimental effect on the performance of production environments.
  • While it is theoretically possible to create a chain of up to 32 snapshots, VMware recommends a maximum of 2-3 elements in a snapshot chain. The consistency of the data and the performance of the environment may no longer be stable at higher numbers.
  • A single snapshot should generally cover no more than 72 hours. Otherwise, the snapshot will be so large that it would take too long to play it back on the original hard drive.
  • ESX / vSphere snapshots grow in increments of 16 MB and can thus reach or even exceed the size of the original virtual disk. If the virtual machine is an email or database server, i.e. a system with drastically high change rates, the size of snapshot will quickly reach the size of the original virtual disk.


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