Talk:RAID/Archive 1

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Removed the link to http://www.wiebetech.com whitepaper

Tried to calculate the failure probability. But this is no scientific paper, the numbers are made up (experience from reality). It's useless and more of a advertorial anyway.

Apu Nahasapeemapetilon

i would change it but i dont know who the original guy is... or is Apu Nahasapeemapetilon right?

questionable links

anyone curious whether or not some of these links meet WP guidelines on external links? Some of these are blogs, and others are of dubious origin. comments? anyone think some of them should go? // 3R1C 22:49, 22 December 2006 (UTC)

still way long

he article is rather unsightly =\ suggestions? 3R1C 15:41, 15 November 2006 (UTC)

Maybe a separate page for each of the RAID levels? Poweroid 17:18, 15 November 2006 (UTC)

Sounds fair to me, but I've put nothing into this article, and I would not feel comfortable just subverting someone elses work =P 3R1C 14:59, 18 November 2006 (UTC)

I agree. A seperate article describing the different types of RAID would be the best solution. A brief explanation of the most common types, 0 and 1, should be all that's left in this article, along with a link to the 'Types of RAID' page for more information. Walther Atkinson 21:44, 15 December 2006 (UTC)

I quite like the article as it is. It may be long, just looking at the word count. On the other hand, just cutting it into different articles makes it even less clearly aranged and concise. Leave it as it is. Johannes121 17:01, 30 November 2006 (UTC)

I I was thinking. In fact, all that needs to be done is to create a simple table under a section called "RAID Levels". Each raid config (RAID 5, etc) would be listed there, hyperlinked to the article that corresponds. (And yes, the current raid level summaries would be moved. -GUEST on 12/1/06

I think it could be simply split into these separate pages:

RAID

contains: History, RAID Implementations, Hardware vs. Software, etc... in other words, the current sections 1,2,6,7,8

what the other Guest said about a table, containing each configuration name and diagram/summary.

(perhaps even make separate pages that go into more detail over each RAID config, but keeping the original "umbrella section" pages)

Standard RAID Levels

Nested RAID Levels

Proprietary RAID Levels

Also, it would not be difficult to split this article up, as all that is necessary is creating more article pages and cutting and pasting articles from this original article to it's new home. Basically, the wiki community just needs to decide on how to split it.) --DEMONIIIK 07 December 2006

then everyone should grab a section and split it. I'm going to go ahead and do one of em now Standard, Nested, and Proprietary sections split. // 3R1C 00:56, 19 December 2006 (UTC)

removed link

removed link, its outright wrong, ad infested and hinting corporate slant. I've studied this and worked with raid 0s and 1s for ages and none of that article rang true.

Confusing Passage

The paragraph below doesnt' make sense somehow. I can't tell if it means there is performacne enhancements to be gained from RAID 1 and 2 or there is not. The advantages of using RAID1 or RAID2 are that if a single disk fails you can use the other disk and no data is lost, and, because two disks are being used at the same time, the throughput is doubled - resulting in a highly noticeable decrease in access times for the disks which greatly adds to performance of the system. Therefore, each disk in the system is independent and there is no increase in performance. In this configuration "independent" or "inexpensive" depends primarily on perspective and either use of the word is correct.

Also, the Raid0 section is poorly written.

reliability

Possible error

With RAID 1, MTBF ought to be the square of that of the individual disks, not double.

Secondly, theoritically the RAID throughput performance can be doubled. But in practicle, RAID 3++ would slow down the performance especially with large files such as database. I'm not talking about Oracle database only, but also mySQL and other kind of files with large partition size. For example, emails and Images storage.

--19:16, 13 April 2006 (UTC) : din

Product of the MTBF's, actually; the disks aren't required to be an exact match.
--Baylink 17:47, 5 September 2006 (UTC)

Reliability scaling.

Guys, isn't a probability of two simultaneous events a product of the probabilities of the independent events. I this light I don't think that reliability of RAID-1 increases linearly with the number of disks.

Agreed. And in the previous sentence, assuming reliability is the opposite of failure, the probability of non-failure is (1 - (pr(n of n drives fail) = pr(single disk failure)^n)). In the given example, going from one to two drives, reliability goes from 1 - f to 1 - f^2, instead of "increasing by a factor of two." In general I think this article leaves a lot to be desired as far as the mathematics of performance and reliability or RAID go. Psyno 23:05, 9 July 2005 (UTC)

It's important to make the distinction between "the odds that one drive in an array will fail" which go up as the number of drives, and "the odds that the array itself will fail", which, indeed, go *down* as the number of drives. The mathematical portions of the piece do indeed need to be cleaned up.
--Baylink 17:49, 5 September 2006 (UTC)

Reliability

I wonder if we should include a section on the misunderstandings people have about RAID reliability. I would hope most people who set up RAID arrays for specilist purposes know what they're doing but a lot of people who do it for fun (or whatever) don't appear to comprehend what RAID (esp 1 and 5) does and doesn't do. Surprisingly a lot of people seem to think it is a good 'alternative' to a backup and fail to understand why 2 hard disks failures more or less simulatenous is not that unlikely (power supply failures etc) and that RAID also doesn't help in the event of natural disasters, viruses etc (of course backups may not help either depending on where you store them). Also when it comes to performance (of RAID 0) perhaps again we should elaborate on the performance advantages (e.g. discussing why 2 disks does not mean double performance in all cases due to the importance of caches, seek times etc for non burst reading) and describe why RAID 0 is not always the best solution for performance reasons (independent disks are probably the best option for most general users) Nil Einne 21:09, 29 March 2006 (UTC)

I agree. As mentioned in my response to RAID 6, it might be useful to create a Code Theory section that goes into the advantages / disadvantages for the different types of RAIDs and why certain mechanisms were created.

Pyth007 19:31, 13 April 2006 (UTC)

Yes, if we *assume* that disk failures are independent, then (in theory) the probability of both drives failing in RAID 1 is much less than the probability of just one drive failing. However, in practice, "those with RAID 1 are marginally *more* likely to lose data than those without any RAID at all." -- http://www.bestpricecomputers.co.uk/reviews/home-pc-raid/ (2005)

I'd much rather this article clearly state what *actually* happens, rather than give some theoretical formula that has nothing to do with the real world. -- User:DavidCary --70.189.73.224 03:31, 30 May 2006 (UTC)

Yes people who use raid 1 as a substitute for rather than in addition to backup are likely to get burnt (and including a warning of that would be a good thing) and many people use raid 0 even though it brings them no real benifit (that article admits is *IS* good for is applications like video when you need to move shitloads of contiguous data arround). But the fundamental premise being pushed by that article that raid itself sucks is just BS. And a raid controller failure shouldn't be an issue for a raid 1 setup (it could well be for a raid 0 or parity based raid though and its something to resarch carefull). Plugwash 01:10, 31 May 2006 (UTC)

This article needs work

Everyone here should read PCguide.com's section on RAID [1] -- it explains it much better than the user who tried really hard to write the article on wikipedia did - sorry dude. Note that ACNC's website's description of RAID 1 is really RAID 1+0 -- RAID 1 must be exactly 2 disks.

RAID 1 is mirroring and doesn't necesarily limit the number of mirrors, though 2 is by far the most common number and certainly it's what I normally think of. Still, there was consideration of using a 3 or more disk RAID setup to help the seek rate of Wikipedia at one point. Jamesday 21:33, 19 Jul 2004 (UTC)

Reworked entirely!

OK, someone else started the new stub, and I added lots more info. Then I went back and diffed the original (infringing) article and put in all the text since then wherever I felt it belonged. So the new Temp stub is ready to roll! --Sfoskett 21:38, 12 Jul 2004 (UTC)

The possibly infringed palce was [2] by a more direct link. I'll also review the article sometime in the next week or so. Jamesday 21:33, 19 Jul 2004 (UTC)

Rework Diagrams?

Does anyone mind if I rework the diagrams from ascii into something more readable, such as a couple of PNGs? The only problem I can see is that a PNG would be harder to repair if I copied a mistake from these ascii diagrams. If anyone who knows what they are doing can confirm that these diagrams are okay, it'd be much appreciated --huwr 08:25, 29 Jul 2004 (UTC)

Considering that a year later we still have the same ascii diagrams, you never got around to making new diagrams. Since your comment you and others have fixed to diagrams so I figure they're probably right by now. Taking into account the fact that I have nothing better to do, I'll make them and post a link when I'm done for peer approval.--Kryptknight 01:57, July 23, 2005 (UTC)

Here's what I've got done so far, it might not be correct procedure to put these images on the talk page as opposed to linking to them but I'm way to tired to look it up or figure out how to link to an image. If it's wrong, anyone has my permission to fix it.

I added a diagram and expanded a couple of others. --Avernar 04:42, 23 July 2005 (UTC)

Raid-6 is wrong. You can't be blamed, our article was vastly incorrect for more than a year. I've corrected the article. --Gmaxwell 05:44, 22 September 2005 (UTC)

--216.232.71.212 04:42, 6 October 2005 (UTC)

The main article is currently using ascii diagrams, and the multi-coloration of the above images detracts from communicating-across the concepts... I would be willing to spend a few minutes and make some jpeg's in M$paint. Optimally, we should use the diagrams from http://www.acnc.com/raid.html, but they are undoubtedly copyrighted. A recreation of them (in differrent colors, different style of arrows, perhaps?) would be what i would aim for. The7thone1188 21:56, 3 June 2006 (UTC)

The ASCII diagrams are incomplete in that they fail to convey parity source, while the colors do this quite admirably. I think it would be a great addition. Dr1819 13:51, 10 June 2006 (UTC)

Also, the AC&NC depiction of [RAID 10]is incorrect (and yes, they're undoubtedly copyrighted). And I disagree with their recommendations and comments as well, particularly on RAID 6's dual parity. The claim it's slow, yet controllers with one chip to generate XOR parity and the other to generate the RS code, the only additional performance hit comes from writing the parity twice instead of once. Dr1819 14:35, 10 June 2006 (UTC)

Vandalism

What is up with all the vandalism of this particular item? I have 1,000 articles in my watchlist, and none is vandalized as often as this one. And the vandalism is just stupid - bold text, added leQtters, inserted single POOP words. Is this used as a sample page somewhere? Is it some newbie ICE-CREAM (original: initiation) course? I hope we don't have to lock it down... --SFoskett 18:02, Sep 16, 2004 (UTC)

I too have seen quite a bit of vandalism on this item. It is beginning to get to the stage where more work is done undoing vandalism than improving the article. --huwr 23:46, 17 Sep 2004 (UTC)

Not sure if it's still going on occasionally, but if this is a problem a tip is to use this Google query: link:http://en.wikipedia.org/wiki/Redundant_array_of_independent_disks. This will perform a Google search on pages linking to this article. I actually found a bunch when just trying it out, but I couldn't see any high traffic sites at a first sight, but I could be wrong. -- Jugalator 00:24, July 25, 2005 (UTC)

Now, sure, it doesn't happen NEAR as often as it used to (I'm guessing...), but... perhaps it is time to just semi-lock it. After all, if someone wants to actually make an intelligent change, it's not exactly impossible to either request a change or just sign up, edit an unlocked page successfully, and wait a week. Let's do it! (By the way, I decided to make SFoskett's post more exciting by adding the other three examples of vandalism to his comment... teehee...) --DEMONIIIK 05:34, 22 February 2007 (UTC)

Why all the vandalism? what do people have against raid arrays? Royallywasted

More vandalism in the form of "Nates gay". Vandals has bad grammar. -- Gnomeza 18:34, 13 September 2007 (UTC)

Irrelevant

The wikilink irrelevant in the sentence "RAID-0 is useful for setups such as large read-only NFS servers where mounting many disks is time-consuming or impossible and redundancy is irrelevant." redirects to Renormalization group which is something not related to the meaning of irrelevant here. --ReiVaX 19:43, 14 Oct 2004 (UTC)

I'm pretty sure that the RAID-6 discussed in the "RAID-6 section" is very different from the RAID-6 discussed in the "double parity" section. I don't really know which is right. 204.0.197.190 20:59, 4 Feb 2005 (UTC)

You need add more RAID levels

You guys need to add more raid levels in "Nested Raid" on RAID 60, RAID 61, and RAID 50.

External links deleted?

Why exactly were the external links deleted in this revision? --Damian Yerrick 23:52, 21 July 2005 (UTC)

Looks like someone removing useful information - I noticed that both of the other removals by that IP had already been undone. I've added back the external links and categories. Jamesday 13:31, 23 July 2005 (UTC)

I'd like to know more about RAID 1 writing

This is what I saw the article had to say about RAID 1 writing:

When writing the array acts like a single disk as all writes must be written to all disks.

It's seriously not too much ;-), and I was particularly wondering if RAID 1 writes were done in parallel or sequentially. I.e. is the writing time of complexity O(1) or O(n) where n is the number of drives? Does it differ between RAID controllers? This may apply to other RAID modes; I haven't checked that far as I was mostly interested in RAID 1 for a possible future computer for now. -- Jugalator 00:28, July 25, 2005 (UTC)

Yeah, I should expand on that. Ideally they writes are done in parallel. There are several things that can force the transfer of data to the drives to occur sequentially. A poor controller design will do it. If both of the drives are on the same IDE cable. For SCSI the transfer over the bus is done sequentially but since this is so much faster than the drives can write to the platters the writes are overlapped:

Disk1:  TTWWWWWWWWWWWWWWW
Disk2:    TTWWWWWWWWWWWWWWW

Where T = SCSI bus transfer and W = Disk Write

This applies to reads as well and the other RAID modes. When I add this to the article I'll probably put it up in the common section. - Avernar 04:36, 25 July 2005 (UTC)

Raid 6 vs Double Parity

The current RAID6 sections descibes double parity. It describes a system in which the folowing blocks exist (but are not shuffled in this fasion):

A1  A2  A3 PA
B1  B2  B3 PB
C1  C2  C3 PC
P1  P2  P3 --

where:

PA= A1 XOR A2 XOR A3
PB= B1 XOR B2 XOR B3
PC= C1 XOR C2 XOR C3

P1= A1 XOR B1 XOR C1
P2= A2 XOR B2 XOR C2
P3= A3 XOR B2 XOR C3

(in reality other parity system may be used, but XOR works perfectly well)

Anyway that is taking parity in two different directions which is what the Double Parity section claims makes it different from RAID-6. That section claims Raid-6 has parity in only one direction, but with two copies. I suspect that is correct and the author of the RAID-6 section was just confused.

UGH! no this is completely an utterly wrong. Raid-6 is an implimentation of Reed-Solomon erasure codes. It turns out that xor is a perfectly valid syndrome for a RS code, so raid-6 just adds another non-overlapping syndrom. Sadly the extra syndrome is much more expensive to use than XOR. Raid 6 is striped exactly like raid-5, except there are two parity blocks to distribute. The system proposed would not handle a two disk failure. Raid-6 does. And RS codes can be generalized to handle any number of redundant disks, and as long as their failure is detectable, as many disks can die as there are redundant ones. --Gmaxwell 04:11, 22 September 2005 (UTC)

and here, I found a citation [3]. --Gmaxwell 04:14, 22 September 2005 (UTC)

I've corrected the nonsense in the page. --Gmaxwell 05:42, 22 September 2005 (UTC)

Meaning of RAID

On a slightly less technical issue, there seems some confusion over the possible meanings of the acronym RAID. At the start of the article it says that "Redundant Array of Inexpensive Disks" is simply incorrect. Later it becomes clear that it is the original meaning, and later still it appears that it may be correct after all. (As usual, I suspect this is a side-effect of multiple editors working on the page.) Could someone sort this out, please?Jon Rob 08:33, 17 November 2005 (UTC)

The use of the word "incorrect" is incorrect, since the original paper was "A Case for Redundant Arrays of Inexpensive Disks (RAID)". Shawnc 14:37, 25 November 2005 (UTC)

I also learnt that it was "Inexpensive" from work/manuals/the MSCE course and I was rather shocked to see it linked from google as independent (why I followed the link) so I'd like to see "Independent" removed or it changed to state that RAID is commonly called "Redundant Array of Inexpensive Discs." (Note that Array is not plural either - is this correct?) eps 13:58, 2 February 2006 (UTC)

---

Also I don’t understand (and thus a good point to add to it), how RAID can actually be called "Independent". Considering its a backup system, and the disk do anything but operating independently. Also the term "Inexpensive" is the original term used by the guy who invented it. Saying that the term inexpensive is not used because hard drives are cheaper is moronic. The idea came about because SLED (Single Large Expensive Disk), was indeed expensive (and obviously still is) and offered no redundancy.[4]--TheWickerMan 02:42, 18 November 2005 (UTC)

---

The disks are considered independent in that they are more independent than would be several platters on the same spindle. That said, I'm not defending "independent" over "inexpensive" -- I'd prefer the original nomenclature as well. Just like a DVD is NOT a "Digital Versatile Disc". Ugh. Drives me nuts. --Stevestrange 22:56, 16 December 2005 (UTC)

RAID 100 diagram

There is an apparent controversy over the RAID 100 diagram. Here's what I think it should be, as per this revision:

                                RAID 0
               /-------------------------------------\
               |                                     |
             RAID 0                                RAID 0
       /-----------------\                  /-----------------\
       |                 |                  |                 |
     RAID 1            RAID 1             RAID 1            RAID 1
   /--------\        /--------\         /--------\        /--------\
   |        |        |        |         |        |        |        |
120 GB   120 GB   120 GB   120 GB    120 GB   120 GB   120 GB   120 GB
  A1       A1       A2       A2        A3       A3       A4       A4
  A5       A5       A6       A6        A7       A7       A8       A8
  B1       B1       B2       B2        B3       B3       B4       B4
  B5       B5       B6       B6        B7       B7       B8       B8

It has since been altered in subsequent revisions. I claim this revision is incomplete because a RAID 100 is definitely a stripe of a stripe of mirrors; that is, a stripe of RAID 10s, rather than a simple RAID 10. It was then (and is currently) deleted altogether. I think the diagram should be included for clarity and completeness, but I'd like not to get into an edit war over it. mAtt 21:07, 22 December 2005 (UTC)

No additional input in five days; I'm reinserting the above diagram. mAtt 20:27, 27 December 2005 (UTC)

Raid 1.5

Raid 1.5 is not described properly. Raid 1.5 has mirroring, striping, and parity for two disks.

Marketting gimmik. You can't mirror and stripe with only two disks. If you stripe half the disk then mirror each block to the other disk you just end up with mirroring with a different on disk block order. As for parity with two disks once you mirror you don't need to also add parity. The DFI documentation does not mention parity, only "stripping and mirroring simultaneously using two drives". Please show me a diagram of the on disk block order of how this is done that's not just RAID 1 with a different block order (the free disk space available with RAID 1.5 is the same as RAID 1). It's only available on two DFI motherboards that are being phased out. BTW, nowhere on HighPoint's site can I find any mention of RAID 1.5.

Avernar 18:43, 9 April 2006 (UTC)

Plagiarism? RAID 1

The RAID 1 section has the same content as the RAID 1 section on http://www.aaa-datarecovery.com/raid_tutorial.htm. I'm not sure who copied from whom. --Westonmr 20:31, 16 January 2006 (UTC)

I'm guessing the external site copied from Wikipedia. The WP page got to that particular revision slowly; if it had been copied and pasted there would have been an edit changing the entire RAID 1 section. There's a similar situation with the external page's RAID 0, JBOD, and RAID 5 sections, and arguably some others as well. I don't think there's a reason to change anything about WP's current revision, and I claim that aaa-datarecovery.com is being Bad. !mAtt™ 21:07, 16 January 2006 (UTC)

More types of RAID

I would like to Know if a 'spanned volumes' is the same as JBOD? --Ed Fraser

new Raid!!

There is a new Kind of Raid we got to add!! Its RAD150!! Also Known as 1+5+0! My ThunderRaid controller onboard SATA does it! It special feature, multi-nested-levels, Data is Striped over distributed parity arrays over Mirrors! Very clever feature. Also popular with Linux Experts!!!

Why not add it then? The entire point of wiki is to allow new information to be added quickly by anyone, yes? There's already a section on nested RAID levels and one for Proprietary levels (not sure which this is). Although I'd advise you avoid the excessive exclamation marks on the actual wiki node or it'll just get deleted ;-) Darksidex 12:14, 26 July 2005 (UTC)

Listen. You need to update this Raid Info. For I have a tech who saying he Know it all from your website. But there New Type of raid. Like the Onboard raid where the controler Use that can use one Hard drive. Like the MSI MS 6380 Promise 20265r Onboard Raid. This guy keep going Only a raid controler can run Only 2 hard drives and I told him Mine runs one. Its called single drive stripped array. Its so if Like me who has too many things on My 4 Ide cable which are full. but have one more hard drive. So Please Update Your info. I can run One, Two or three or Four hard drives. See I know this is not the 15 hard drives your talking about but the Onboard hard drive a motharboard would have.

You can have an array of any number of volumes you like on a single drive, but from any practical point of view you like to name, it is utterly pointless. It reduces performance by a massive amount (because of dramatically increased access times), and also decreases reliability (because RAID volumes are always more fragle than a single volume). In fact, the only thing it increases is the cost. Tannin 09:38 20 Jun 2003 (UTC)

On another topic, the first sentence of the article reads, "The goal of a redundant array of independent disks (originally known as a redundant array of inexpensive disks) -- or RAID -- is to provide large reliable virtual disks that can be much larger than commonly available disk drives."

After "much larger", I would add the words, "and more reliable".

--Gil Dawson

Discussing the characteristics of RAID 1, "One write or two reads possible per mirrored pair. Twice the read transaction rate of single disks, same write transaction rate as single disks."

I wonder if the terms "read" and "write" might not be backwards? Seems that one read would be sufficient, while two writes would be required.

--Gil Dawson

No, it's correct that reading is twice as fast and writing is about the same speed. The reason is because the drives are capable of working simultaneously. Thus the same write can happen twice on both drives. Reading though, gets a speed boost because it can be distributed allowing each drive to read different parts of a file simultaneously and combining the parts in memory.

--Rev. Johnny Healey

would RAID-53 count as one of the RAID levels? Not too sure... searchstorage RAID definition includes raid-53 Applegoddess 04:42, 9 Jun 2004 (UTC)

Style

The various levels of RAID would be easier to understand if the main article used 1+5+0 et cetera rather than 150. 150 could easily be confused with something else that uses the number 150, and wouldn't imply the nesting/adding of levels. Last Avenue 01:02, 27 January 2006 (UTC)

Am I the only person who thinks the jump into the rather terse discussion of Reed-Solomon code in the section for RAID 6 is jarring? I dosen't seem consistant with the other sections. Surely it's useful information, but perhaps not at the beginning of the section.

For the numbering style of nested arrays, I believe that the heading for RAID 50 was designed best. It provided the more common single number as the main term, but kept the 5+0 style for ease in understanding the semantics.

As for the Reed-Solomon discussion, I agree that article went from a fairly basic discussion of RAID technologies and suddenly plunged into code and number theory. Perhaps moving these two paragraphs to the end of the RAID 6 section would feel less jarring. Alternatively, a Coding Theory section or moving the Reed-Solomon paragraphs into the History section may be more suitable. Have the History go through disk-mirroring and pre-RAID ideas, then move into discussing classical RAID technologies with parity and striping, and finish the History section with "modern" approaches like RAID 6 and nested arrays, using the coding / number theory to show reasons for these new arrangements. (I actually like this best, especially considering that the Reed-Solomon paragraphs begin by considering the RAID 5 paradigm and extend it to RAID 6)

Pyth007 18:31, 13 April 2006 (UTC)

JBOD

JBOD -- this is, as far as I know, just a bunch of disks, not a neccessarily a concetination. There are many RAID controllers available whose vendors claim they are able to do "raid 0, raid 1, raid 5 and jbod" or so, and they mean: The read controller can act as a non-raid hard disk controller, giving access to each of the disks individually. There are many wrong definitions of this term out there and JBOD may be used for concatination, too, but I think the term is much more unclear than stated in the article. Right? Kruemelmo 15:17, 30 January 2006 (UTC)

No, JBOD is concatenation. Running a RAID controller in non-RAID mode as a normal controller doesn't have a special term.

Avernar 19:02, 9 April 2006 (UTC)

Citation, please? My experience, too, is that JBOD is most commonly used to apply to a bunch of drive hanging in a RAID-style rackshelf, but which are just on a controller channel and being used for non-RAID purposes. The configuration the article currently mentions is really a longitudinal stripe, and therefore, probably a variant of RAID 0.
--Baylink 17:42, 5 September 2006 (UTC)

Trying to find a good citation on the net about JBOD is a pain in the butt. The best info seems to be in the newsgroups (usenet). The info I have found basically says that when people talk about a raid controller card and what modes it supports JBOD means spanning. When people talk about storage array boxes like SANs it can also mean non-RAID/non array disks. And the high end raid card manufacturers use the second meaning (since they also do DAS/NAS/SANs). No wonder there's so much confusion about what JBOD means: it has two meanings.

We can change the section title to Spanning/Concatenation and put in the text that it's usually called JBOD and make another section for JBOD as well. Or we can put both meanings in the same section. Which one sounds less confusing?

Technically there's nothing wrong with our description as a single disk is just a span of 1 disc. Looks like some storage boxes use this definition as well as you can have individual disks or concatenation in their JBOD mode. Interesting piece of information I found: someone mentioned that when he was using JBOD mode on his controller the drives showed up as RAID arrays of 1 disk each, but when he turned RAID off they showed up as normal SATA drives.

Avernar 09:18, 28 October 2006 (UTC)

The article is giving people to much hope when it comes to recovery after a failed disk in JBOD. The data on the other disks will be there, but the file system will most likely be a mess, so they may be very difficult to recover. KNaranek

Regardless of which definition is correct, there should be some definition included, or the redirect corrected, as currently JBOD redirects to this article, and yet the article makes no mention of the term.--Tmetro 17:58, 25 December 2006 (UTC)

Who introduced the incorrect information about JBOD?!

There is now an entire section of this article which is incorrect.

JBOD is not a RAID mode -- it is the opposite. It literally means the disks are not acting a set -- not even a linear concatenation.

Also, concatenation is a RAID mode -- it is just a special case of striping where the width is the same as the volume.

Is there some debate on these points or can it be changed immediately?

When talking about RAID modes JBOD usually means concatenation (spanning). Yes, it's not an official raid mode. It's not redundant but neither is RAID 0.

When talking about storage in general, like SANs for instance, JBOD can refer to the discs as not being part of an array. A lot of people who deal with big data storage use the term this way.

Concatenation is not a RAID mode. It is not a special case of striping. You can't set up a raid controller in RAID 0 mode with a block size that big. Even if you could it wouldn't be the same on disk layout as JBOD with different size disks. The size of the smallest disk would be you're first set of stripes and then the remaining space would be striped next if the controller can do it, otherwise it would be wasted. JBOD doesn't waste space with disks of different sizes.

I don't believe that the section should be replaced. Perhaps we should rename the section to Concatenation/Spanning and put in the text that this is called JBOD when people talk about raid modes.

Avernar 06:33, 28 October 2006 (UTC)

JBOD does not mean spanning or concatenation. JBOD means 'just a bunch of disks' Any indutrial RAID controller I have used (and I work with them every day in R&D) will simply provide a single physical disk if you assign it as a JBOD.

Baz whyte 19:57, 26 February 2007 (UTC)