Talk:RAID/Archive 1

message: 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)
thread_title:  questionable links 

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

message: 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)
replies: text: 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)
thread_title:  Reliability scaling. 

message: Everyone here should read PCguide.com's section on RAID  -- 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)
thread_title:  This article needs work 

message: 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)
replies: text: The possibly infringed palce was  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)
thread_title:  Reworked entirely! 

message: 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)
thread_title:  Irrelevant 

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

message: 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)
thread_title:  I'd like to know more about RAID 1 writing 

message: 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)
replies: text: and here, I found a citation . --Gmaxwell 04:14, 22 September 2005 (UTC)

text: I've corrected the nonsense in the page. --Gmaxwell 05:42, 22 September 2005 (UTC)
thread_title:  Raid 6 vs Double Parity 

message: 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)
replies: text: 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)
replies: text: 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)
thread_title:  Meaning of RAID 

message: 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)
replies: text: No additional input in five days; I'm reinserting the above diagram. mAtt 20:27, 27 December 2005 (UTC)
thread_title:  RAID 100 diagram 

message: 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)
thread_title:  Raid 1.5 

message: 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)
replies: text: 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)
thread_title:  Plagiarism? RAID 1 

message: 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)
replies: text: 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)
thread_title: More types of RAID