RAID MD10

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I’m going to rebuild my system at home soon, and was planning to mirror two drives. However, I was just looking up something about RAID, and on wikipedia found some information about the Linux MD driver, and “near” and
“far” RAID10.

Anyone have some opinions about them?

mark “or should that be how many opinions do folks have
about them?”

8 thoughts on - RAID MD10

  • Raid 10 is a mirrored stripped set of at least 4 driver. You get the best of both worlds, data speed and data back up..

    john

  • yeah, that’s the industry standard. he’s asking you to go find and read http://en.wikipedia.org/wiki/Raid10#Near_versus_far.2C_advantages_for_bootable_RAID
    wherein they mention that linux md devices can do what they call a raid 10 on 2 drives. and then details some of the reasons you might want to do such a thing.

    I can’t see any reason to go with the sorta raid 10 on only 2 drives. from that article, I’d the only sane choice for raid 10 on 2 drives is the ‘far’ config on SSD drives. but that’s just my opinion. I
    don’t think I’d ever pick raid10 on 2.

    from the entry:
    “…copies of a block of data are “near” each other or at the same address on different devices or predictably offset: Each disk access is split into full-speed disk accesses to different drives, yielding read and write performance like RAID 0 but without necessarily guaranteeing that every stripe is on both drives”

    which then some (and by murphy’s rule will be the most critcal) will go from being raid 10 to raid0. and likely 0 on the drive that fails.

  • right, thats the industry standard RAID-10

    this case is around the non-standard mdraid10, which can do a bunch of interesting things on 2 ( but really 3 disks ) or more.

  • zGreenfelder wrote:

    AHHH! I didn’t read closely enough, and missed that lack of guarantee. Thanks, *that’s* the kind of discussion I was looking for.

    mark

  • You can of course build a layered raid 0 above some raid1 arrays, but linux md raid10 is another beast. Actually you can build a raid10 with only 2 disks. The theoretical benefit is that is is striped, so even one single process benefits from it. If you use raid 1 a single process does use only 1 disk as far as I know.

    http://en.wikipedia.org/wiki/RAID#Non-standard_levels

    One disadvantage is that you can not grow or expand it easily, which means it is inflexible, which is why did not want to use it.

  • The storage industry tends to use “RAID 1+0” when they specifically refer to the older striped sets of mirrors. RAID 10, as implemented under Linux is also found in some high end RAID controllers. Among other things, it will allow you to have a RAID set with an odd number of devices, and ensure that all of the stripes are on two different disks.

    The description of Linux RAID10 on the wikipedia “nested raid levels”, referred to by zGreenfelder, was probably written by someone unfamiliar with the topic. I’m not able substantiate a number of the claims made therein. I wouldn’t rely on that information.

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