Talk:RAID

RAID was nominated as a good article, but it did not meet the good article criteria at the time (No date specified. To provide a date use: {{FailedGA|insert date in any format here}}). There are suggestions below for improving the article. If you can improve it, please do; it may then be renominated.

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19 October 2007

RAID0 contradiction

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Any disk failure destroys the array, which becomes more likely with more disks in the array. A single disk failure destroys the entire array because when data is written to a RAID 0 drive, the data is broken into fragments. ... When one sector on one of the disks fails, however, the corresponding sector on every other disk is rendered useless because part of the data is now corrupted.

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Does a sector failure destroy just data from corresponding sectors, or from the entire array? It's not entirely clear at the moment. --Tom Edwards 15:02, 20 October 2007 (UTC)[reply]

RAID 1

"Provides fault tolerance from disk errors and single disk failure..." Correct me if I'm wrong, but if more than 1 disk fails in a RAID 1 of more than 2 disks, can't it still recover from the failure since they are all mirrored? Viper5030 (talk) 18:21, 5 December 2007 (UTC)Viper5030[reply]

You mean if disk 1 mirrors disk 2 and disk 3 mirrors disk 4. In that case yes, unless two in a pair fails. But it's arguable that they're two independent raid systems, and then no.- (User) WolfKeeper (Talk) 19:06, 5 December 2007 (UTC)[reply]

Speaking theoretically it is a case of a replication-based fault-tolerant system in which a majority quorum is used to determine "which value is correct?" RAID has absolutely zero guarantees on data integrity so it is possible for both drives in a 2-disk RAID 0 to have the exact same error and you will not see an error produced by the RAID system: the data matches. (That's assuming it checked for equality to being with, which I think is a false assumption).

So if you had a 5-disk RAID 0 you could assume that if 3 or more drives read the same value then that is the correct value. If you have 3+ drives online still then you could assume that they hold the right value if they all match. If you have a 4-disk system and 2 fail then you have no majority of disks to "vote" on the correct value.

Of course, this assumes that the RAID controller verifies correctness across drives on read. With RAID 0 you can always recover from any number of lost disks provided you have at least one drive standing (just re-mirror it!). Just hope that that one disk hasn't been corrupted in any way. Cburnett (talk) 20:50, 5 December 2007 (UTC)[reply]

RAID 2

Where is RAID 2 (parity via hamming codes)? —Preceding unsigned comment added by 69.202.78.173 (talk) 01:46, 24 October 2007 (UTC)[reply]

RAID 4 & 5 minimum disk amount wrong

While useless, you can run RAID 4 & 5 on two disks. This is, in effect, RAID 1. -- RichiH 16:43, 30 October 2007 (UTC)[reply]

...and I think for that reason it is not appropriate to describe 4 & 5 as being possible on 2 disks. Put another way, it is not helpful to describe these logical niceties, it simply confuses. Spenny 17:14, 30 October 2007 (UTC)[reply]

RAID 2

RAID 2 should be included in this page Although RAID 2 doesn't really have any commercial implementation, I think the article should give the reader a good overview of the different RAID implementations, adding RAID 2 will make that overview better.

As said below: RAID 2 uses Hamming codes (wiki article available) to do error checking. Other than that, RAID 2 is very similar to RAID 3. The reason why RAID 2 hasn't been a commercial success is because of the fact that using Hamming codes as error checking mechanism requires a great deal of disk space (also the raid controller has to perform complicated calculations to do the error checking).

I'm certainly not an expert on this issue, so somebody with more expertise should verify this and maybe add some good structured text about this to the article. —Preceding unsigned comment added by 143.129.41.95 (talk) 14:47, 5 November 2007 (UTC)[reply]

[RAID0] Number of disks

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...RAID 0: Striped set (minimum 2 disks) without parity...

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Is possible use 3 disks to make a RAID 0? Or is necessary couple numbers (as 2, 4, etc)?

18:39, 4 December 2007 (UTC)Renato S. Yamane

Any number would work. For 3 disks: blocks 0,3,6,9 would go on disk 1; 1,4,7,10 on disk 2; and 2,5,8,11 on disk 3. Cburnett 19:08, 4 December 2007 (UTC)[reply]

[RAID0+1, 1+0] Number of disks

The article says that minimum 4 disks are required, however it is possible to use in a two-disk scenario. This is used for example in HP Proliant DL320 G4, which can only house two disks. —Preceding unsigned comment added by 213.112.31.36 (talk) 13:14, 8 January 2008 (UTC)[reply]

Fake RAID: hardware or software?

I think this edit in incorrect, because the paragraph starting with Since these controllers use proprietary disk layouts... refers to the one that precedes it, Because these controllers often try to give the impression of being hardware RAID controllers.... I think the real error is that those two paragraphs should go at the end of the Hardware-based section, not the Software-based section. --Fstanchina (talk) 16:41, 27 January 2008 (UTC)[reply]