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I've worked in IT quite a number of years, so I know what a RAID array is, what RAID 0 is, RAID 1, 5, 6, 10, 50, 60, etc., but something sprung to mind in a recent conversation at work; if RAID stands for redundant array of independent (or inexpensive) disks, then why is RAID 0 classed as RAID at all and not just a striped array?

Having data striped across multiple disks on the one array offers no redundancy whatsoever so why is it classed as a RAID array? Surely the lowest number should be RAID 1 (mirrored) as that's when redundancy actually starts?

Peter Mortensen
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Gavin Burke
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6 Answers6

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You actually part answered this in your question.

The lowest form of RAID is RAID 1. RAID 0 was added well after RAID was defined (can't find reference to a date for this though)

The 0 in RAID 0 is used to signify that actually it isn't considered redundant. Think of it as more True/False where 0 is False.

Drifter104
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RAID is just a name with a meaning that changed over time.

The important part is that the underlying technology and mechanisms are the same for the RAID levels, so you use the same controller (or piece of software, e.g. mdraid) to achieve all RAID levels.

Sven
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As others have suggested, RAID 0 could be taken as level 0 meaning zero redundancy. It is referred to as RAID even though there is no redundancy for two other reasons:

  • It is usually defined and talked about in the same contexts, so the name stuck. The same can't be said for JBOD, but such arrangements don't tend to get described along with RAID levels as they have less in common (RAID 0 at least involves striping as found in the likes of RAID 5).

  • While RAID 0 offers no redundancy on its own, it is often used as part of a composite RAID arrangement that does offer redundancy. RAID 10 is the most common, combining 0 for speed with 1 for redundancy. RAID 50 and RAID 60 are less common, but equally valid except where the potential write performance hit (due to 5/6's read-checksum-write pattern) is a concern.

gWaldo
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David Spillett
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Normaly you talk about a RAID Level. So i you say a System is RAID-0 it does not mean it is 'redundant with type 0', it does only mean it is of 'RAID Level 0', witch means no raid at all.

Dieter Meemken
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Because "not redundant" is a valid point on the scale of how redundant something is.

Lightness Races in Orbit
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Pure marketing.

<reminisce> I remember when file servers for local area networks started appearing on the market. And yes, RAID 0 was one of the possible configurations. RAID was such a hefty buzzword at the time that managers would just simply ask "well does the server have RAID?" without knowing exactly what that meant. So the crafty salespeople started relabelling striping as "RAID 0" and thus they could "truthfully" say "why yes it does!" </reminisce>

RAID... it was a punchy acronym. Not like, say SCSI, (pronounced "scuzzy.") It was one of those few acronyms that an IT manager could fling out at a high level budget meeting to dazzle others into approving a purchase. You want to get your slice of the budget pie? You've got to have good acronyms. Just try saying "we've just got to get SCSI" in a meeting like that. See how far you get.

ssimm
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