After many, many articles, discussions, threads, presentations, questions and posts on choosing RAID, I have finally decided to publish my 2012-2013 high level guide to choosing RAID.  The purpose of this article is not to broadly explain or defend RAID choices but to present a concise guide to making an educated, studied decision for RAID that makes sense for a given purpose.

Today, four key RAID types exist for the majority of purposes: RAID 0, RAID 1, RAID 6 and RAID 10.  Each has a place where it makes the most sense.  RAID 1 and RAID 10, one simply being an application of the other, can handily be considered as a single RAID type with the only significant difference being the size of the array.  Many vendors refer to RAID 1 incorrectly as RAID 10 today because of this and, while this is clearly a semantic mistake, we will call them RAID 1/10 here to make decision making less complicated.  Together they can be considered the “mirrored RAID” family and the differentiation between them is based solely on the number of pairs in the array.  One pair is RAID 1, more than one pair is RAID 10.

RAID 0: RAID without redundancy.  RAID 0 is very fast and very fragile.  It has practically no overhead and requires the fewest hard disks in order to accomplish capacity and performance goals.  RAID 0 is perfect for situations where data is volatile (such as temporary caches) and where data is read only and there are solid backups and where accessibility is not a key concern.  RAID 0 should never be used for live or critical data.

RAID 6: RAID 6 is the market standard today for parity RAID, the successor to RAID 5.  As such, RAID 6 is cost effective in larger arrays (five drives minimum, normally six or more drives) where performance and reliability are secondary concerns to cost.  RAID 6 is focused on cost effective capacity for near-line data.

RAID 1/10: Mirrored RAID provides the best speed and reliability making it ideally suited for online data – any data where speed and reliability are of the top concern.  It is the only reasonable choice for arrays of four or fewer drives where the data is non-volatile.  With rare exception, mirrored RAID should be the defacto choice for any RAID array where specific technical needs do not clearly mandate a RAID 1 or RAID 6 solution.

It is a rare circumstance where RAID 0 is required, very rare.  RAID 6 has a place in many organizations but almost never on its own.  Almost every organization should be relying on RAID 1 or 10 for its primary storage and potentially using other RAID types for special cases, such as backups, archives and caches.  It is a very, very rare business that wouldn’t not have RAID 10 as the primary storage for the bulk of its systems.