RAID for Rookies

Sheltering from the RAID

RAIDing for Rookies


As anyone with an interest in enthusiast PCs and hardware will know, acronyms are thrown around hardware circles with more hapless abandon than the viral "... I took an arrow to the knee" Skyrim quote.  The poignant acronym for this article will be... RAID. 

Before we begin, let me just say that you shouldn't be afraid of RAID because it is deemed 'enthusiast' - modern computer systems allow the most complex RAIDs to be setup (far too) easily.  Instead, you should be afraid of how addictive the performance and utility of a solid RAID setup can be!

Historically, RAID was shorthand for 'redundant array of inexpensive disks', however, as our bank managers can attest to, storage media is far from inexpensive.  If you were feeling particularly anal at the time, you could have probably attempted to sue a manufacturer for price misrepresentation! 

On this basis, the term was revised to represent a 'redundant array of independent disks' - cleverly emphasising the combination of multiple, separate, hard-disks without placing an expectation for cost-saving on the part of the consumer.


RAID Overview

So, right about now you'll be wondering what a RAID actually is - physically and logically.  Allow me to elaborate upon these. 

Physically, as the revised acronym allows you to discern, it is many hard-disks operating, logically, in unison as a single storage device.  These disks have commonly been assumed to be identical (i.e. same manufacturer and model) in order to firstly create the array, and for the array to main operable integrity.   This is where raw evidence actually edges towards the 'disproven' camp. 

There are two terms that are important at this point - heterogeneous and homogenous.  The former, heterogeneous, refers to a RAID setup which would be created from multiple different hard-disk drives.  The latter, homogenous, is a RAID setup that would consist of near-identical hard-disk drives.

Several years ago, during the construction of a new-build backup server, I tested the differences between the traditional 'same-disk' RAID and an adhoc RAID, composed of differing vendor hard-disks.  The results were very close - marginal read/write improvements were gained from the same-disk RAID setup, but the difference was slight -  in the order of 25MB/sec average read/write over the adhoc RAID. 

The importance of this factor is impossible to quantify for an enthusiast.  The spare drives you may have access to would inherit cost-saving that could, depending on your goals, far outweigh the marginal 25MB per second read/write decrease you would notice when compared with a pricey new  homogenous RAID setup. 


RAIDing for Rookies"I used to be a rookie until I took an arrow in the... disk-drive" (sorry)


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Most Recent Comments

06-02-2013, 09:41:18

New boy Matt joins the OC3D team and his first article is a Raid Guide. He says "It is time to dispel the mystique around the previously perceived 'hardcore' hard-drive setups..."

Continue ReadingQuote

06-02-2013, 10:26:37

Josh Weston
A great write-up.
Welcome to the team, Matt.Quote

06-02-2013, 10:41:27

Impressive write-up there

However, as an ex-storage consultant, please permit me to point out a few niggles

Page 2 - Raid 5 : You mention "Instead of the traditional mirroring of stripes"... I believe this should read "striping of mirrors" as you aptly described in the Raid 1+0 section above. Remember that striping of mirrors offers greater redundancy than mirroring of stripes (raid 1+0 is better than 0+1).

Page 2 - Raid 6 : The parity is not mirrored, it should be (in any decent implementation) a completely separate parity generation - this offers extra protection against bad blocks that store Raid-5 parity data during rebuild operations.

Page 3 - Mirroring : This attribute offers substantial performance gains for read operations, but none for write operations.

Page 3 - Raid FAQ 1 : Performance improvements are in-line with hard drives, eg: Raid-0 across 2 SSDs will double the throughput in both read and write operations. While real-life improvements may barely be noticeable, the performance increase is real. Also TRIM is now supported in Raid-1, so I argue that wear-rates are not substantially increased over a single SSD. I do agree it rarely makes financial sense though

Raid FAQ 3 : It is very possible to partition your different size drives and then use software RAID across like-size partitions. Leaving you with free partitions you can use for data storage, with the proviso they have no redundancy. Eg: 2TB + 500gb - partition the 2TB into 1.5TB + .5TB, then RAID across the 500gb partition and the 500gb drive. You can subsequently use the 1.5TB partition as normal.

I fully approve of the work you've put in to this and it is overall very good
I am however anally retentive having done this for a living for a while so I hope you'll take my comments as "constructive criticism" rather than any kind of dig

Keep up the good work!Quote

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