Tip

Understanding snapshots and point-in-time copies

What you will learn from this tip: How to perform time-based snapshots and point-in-time data protection, how these techniques differ, appropriate uses for each and some technology examples. (This tip is part of our Storage 101 tip series.)

There are a number of reasons why you might want to utilize snapshot and associated technologies, including the need to simplify and speed up

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restoration after data loss, data corruption or simply forgetting to save something.

Other reasons include making copies of data for test purposes including software development, regression testing and DR testing; making copies of data for application processing including data warehouse, data marts, reporting and data mining; and making copies to faceplate non-disruptive backups and data migration.

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Different applications have varying data protection requirements, including recovery time objectives (RTO), recovery point objectives (RPO) and data retention needs. So how do you know what technique and technology to use for disk-based backup (D2D), mirroring and replication or snapshots? Understanding techniques and the available technology is important; however, it is also important to understand what you are trying to accomplish.

The following are some basic steps and things to consider when evaluating and understanding snapshots and other data protection techniques.

  • Understand the applicable threats to your applications and data.
  • Know your applications and associated data RTO and RPO requirements.
  • Decide who will perform data recovery. How easy should the interface be?
  • Decide how transparent you need your data protection and recovery scheme to be.
  • List the technologies you currently have in place (hardware, software, etc.).
  • Become aware of alternative techniques and technologies for data protection.
  • Figure out your budget, timeframe, tolerance to disruption and risk aversion ahead of time.
  • Decide what you should look for in a solution.
  • Decide which solutions you should use for different applications.
  • Seek out experienced help for assessment, validation or implementation.

    • Snapshot technology in its basic form includes full volume copy, also known as a mirror, clone, or business continuance volume; and partial copy, where only changed data, or pointers to changed data, is kept.

    These two approaches are similar in that they allow you to take a picture, or a copy, of the state of the data on a storage volume at a particular point in time. The differences lie in that a full volume copy is like a picture, and all of the data is copied and represented in the picture while a partial copy is a picture of the changes since the snapshot occurred. There are many different techniques and options for both full and partial snapshot copies, but they vary by vendor and specific product set.

    This concludes the first installment in this series on snapshots and point-in-time copies. In the next installment, we will take a closer look full volume copying and point-in-time or snapshot copying.

    For more information:

    Any-point-in-time backups

    About the author: Greg Schulz is a senior analyst with the independent storage analysis firm The Evaluator Group Inc. Greg has 25 years of IT experience as a consultant, end user, storage and storage networking vendor and industry analyst. Greg has worked with Unix, Windows, IBM Mainframe, OpenVMS and other hardware/software environments. In addition to being an analyst, Greg is also the author and illustrator of Resilient Storage Networks.


    This was first published in August 2005

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