RAID

  • Steve Jones - SSC Editor

    SSC Guru

    Points: 720952

    Comments posted to this topic are about the item RAID

  • Lynn Pettis

    SSC Guru

    Points: 442359

    Very good question. Had to really think about it before answering, and I got it right.

  • M&M

    SSC-Insane

    Points: 21699

    Thanks for the question. Remember reading about it few years back.

    M&M

  • Koen Verbeeck

    SSC Guru

    Points: 258965

    Nice question, thanks.

    Need an answer? No, you need a question
    My blog at https://sqlkover.com.
    MCSE Business Intelligence - Microsoft Data Platform MVP

  • Henrico Bekker

    One Orange Chip

    Points: 27652

    Good question...had a related question in the 70-450 exam last month.

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    This thing is addressing problems that dont exist. Its solution-ism at its worst. We are dumbing down machines that are inherently superior. - Gilfoyle

  • Carlo Romagnano

    SSC-Insane

    Points: 22010

    WOW, I get it right! Today, luck is with me. 😀

  • jts2013

    Hall of Fame

    Points: 3226

    Never heard RAD10 called RAID 1+0 before so I learned something today. Thanks.

  • paul s-306273

    SSChampion

    Points: 10615

    Learnt something new today - and got into top 2000 on QOTD!

  • Koen Verbeeck

    SSC Guru

    Points: 258965

    paul s-306273 (1/26/2011)


    Learnt something new today - and got into top 2000 on QOTD!

    Congrats! 😀

    Need an answer? No, you need a question
    My blog at https://sqlkover.com.
    MCSE Business Intelligence - Microsoft Data Platform MVP

  • paul s-306273

    SSChampion

    Points: 10615

    Thanks Koen!:-)

  • cengland0

    SSCertifiable

    Points: 6102

    Good question today. I almost selected the option saying they have the same tolerance but then had to really think about it. I've lost data using spanned drives so even if that's backed up, you could lose data if one drive fails on the original and on the copy. If you have mirrored data as your original, there isn't any combination where only two drives would cause you to lose your data. So after thinking about it for a while, I did finally select the right answer. It was a close one though.

  • Bob JH Cullen

    SSCrazy

    Points: 2082

    I answered "the same", and was surprised to get it wrong.

    But, having thought more, doesn't the answer depend on how many drives there are? I was assuming four drives, A, B, C and D, as that's the only time I've used RAID10. I'm also assuming the terminology follows this: In RAID 0+1, I stripe A & B and mirror the stripe set onto C & D. In RAID 1 + 0, I have two mirrored pairs, A & B and C & D, which form the two stripes. I have never seen a RAID controller that explicitly states RAID 0+1, so I'm never sure which way round it is handling my four drives.

    In either configuration, you can only lose two disks, and even then only the right two.

    Or have I got it all wrong ... again?!

  • cengland0

    SSCertifiable

    Points: 6102

    Bob Cullen-434885 (1/26/2011)


    I answered "the same", and was surprised to get it wrong.

    But, having thought more, doesn't the answer depend on how many drives there are? I was assuming four drives, A, B, C and D, as that's the only time I've used RAID10. I'm also assuming the terminology follows this: In RAID 0+1, I stripe A & B and mirror the stripe set onto C & D. In RAID 1 + 0, I have two mirrored pairs, A & B and C & D, which form the two stripes. I have never seen a RAID controller that explicitly states RAID 0+1, so I'm never sure which way round it is handling my four drives.

    In either configuration, you can only lose two disks, and even then only the right two.

    Or have I got it all wrong ... again?!

    No, the number of drives doesn't matter.

    Imagine if you lost one drive in the first spanned set of drives and one drive in the second spanned set of drives. All your data is then lost. This doesn't matter how many drives you have. All you need to do is lose one drive in both sets and it's all over.

  • James Lean

    SSCertifiable

    Points: 5697

    I have always been under the assumption that both of these RAID levels can tolerate the same number of failed disks; in theory you can lose up to half the disks from either level, depending on which disks fail.

    In RAID 0+1 you have two stripe sets that are mirrored, therefore you could theoretically lose all of the disks from one of the stripe sets and still have the data available.

    In RAID 1+0 you have a number of 2-disk mirrors that are then striped together. Theoretically you could lose one disk from each mirrored pair and still have the data available.

    -----
    JL

  • Bob JH Cullen

    SSCrazy

    Points: 2082

    cengland0 (1/26/2011)Imagine if you lost one drive in the first spanned set of drives and one drive in the second spanned set of drives. All your data is then lost. This doesn't matter how many drives you have. All you need to do is lose one drive in both sets and it's all over.

    My point exactly. So why is one more tolerant than the other, according to the "right" answer?

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