May 24, 2007

Backups v. Redundancy

What are difference between Redundancy and Backups? Typically, when discussing redundancy in terms of data storage, you are talking about a RAID. Many people make the mistake of thinking that because you have a RAID you have backups of your data, this is NOT true. But to understand why this is not true, you need to understand the differences between Backups and a RAID and what their purposes are.

What is a RAID?

RAID: Redundant Array of Inexpensive Drive

RAID is exactly what it says. It is an array of drives, all of which are typically identical in specs and based on the configuration you set will divide and/or replicate the data you save to them. A RAID can be set up in several ways, but the most typical are RAID 0, RAID 1 and RAID 5

RAID 0, or striping, refers to a configuration in which you have typically 2 hard drive of the same size and you set them to “stripe” data across both drives. It will generally provide for better performance because the computer can read from both disks when searching for data. This configuration provides no redundancy, and a single disk failure will cause the array to fail and data to be lost.

RAID 1, or Mirroring, is the practice of again taking 2 drives, but instead of striping the data across both drives, the drives mirror each other. With this configuration, you lose half your total storage space (because you are basically saving everything in 2 places), but you will get a performance boost because the computer can then use 2 separate points to pull data from, and if one disk dies, the other can pick up where it left off, which provides basic redundancy.

RAID 5, or a striped set, consists of a minimum of 3 disks, which is configured in a way that the data is distributed across all of the drives, and allows for the failure of 1 drive without data loss. The percentage of lost storage space in a RAID 5 configuration varies based on how many total drives there are (e.g. if you have 3 100GB drives, you have 200GB storage space. If you have 5 100GB drives, you have 400GB of storage space)

There are several other configurations for RAIDs which combine the above setups and allow for better performance or better redundancy. But these are the 3 Basic configurations. For more information about various RAID configurations, including options available via software see the RAID entry on Wikipedia.

What are Backups?

Backups are a copy of data, stored for the purpose of having a second copy of an original source in case of loss of the original source. Typically, backups are run on scheduled intervals. The frequency of a backups and how long you keep a backup for depends on the needs of you and your business. In an environment like a bank, backups are taken every few minutes because the number of transactions processed is very large, and the data being processed is very important. For a small business once a week may be often enough for documents that change, and once a month for archived information.

There are several types of Backup configurations and types including Full, Incremental, and differential. For more information in regards to the different types of backups see the Backup entry on Wikipedia

How to Choose:

When trying to determine which solution is best, you need to ask what your needs are. Do you need to have your computer up and running all the time? Or do you need to be able to replace files they may have been deleted, corrupted, or edited by mistake?

If you need the uptime, then a RAID solution is what you need. RAID solutions (with the exception of RAID 0) provide the most uptime, because if one of the hard disks fails, the others can take its place temporarily. If you need to have older versions of documents, or the ability to recover a lost document because it was deleted by mistake, or someone edited it and saved it incorrectly, then you need a good backup solution. And if you are like most businesses, you need both. In which case, you will need a RAID set up as well as a Backup solution.

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