Explain RAID to me.

Posted:
in General Discussion edited January 2014
I always wanted to know. What is it and what does it accomplish/do. I assume it is some kind of hard drive linking/sharing deal?



Thanks in advance.

Comments

  • Reply 1 of 16
    maskermasker Posts: 451member
    if you have one hard drive and need to use an application off of it to create documents (data) then this hard drive is spending time reading and then writing. it can't do both at once.



    With RAID Redundant array of independent drives, you can read and write at the same time. The HD's still work the same way, just while one is reading the other is writing and vice versa. So on particular file is written in small chunks of two different HD's. If one HD fails you've lost all your data. Yuck



    The above is for a striped configuration.



    Raid also refers to having two drives that mirror each other making data loss very rare. These doesn't get you a perfromance increase but it makes your data safe.



    There ever increasing levels of RAID... were drives are sharing data reads/writes and also mirroring each other.



    i think there are 5 recognized combinations of RAID. All striped, or mirrored or some combo of the two.



    MSKR
  • Reply 2 of 16
    amorphamorph Posts: 7,112member
    [quote]Originally posted by SDW2001:

    <strong>I always wanted to know. What is it and what does it accomplish/do. I assume it is some kind of hard drive linking/sharing deal?



    Thanks in advance.</strong><hr></blockquote>



    RAID stands for Redundant Array of Independent Drives. What it does is link two or more physical drives together so that they act like one drive.



    There are two possible benefits to this approach, known as "striping" and "mirroring." If the RAID is striped, that means that data is shared between the drives in such a way that (theoretically) it can be written out and read in at the combined speed of the drives. If it's mirrored, then each drive is an exact replica of the other(s). Then, if one fails, the computer using the RAID can continue as if nothing had happened. If the drives are shared over a hot-swappable bus (FireWire or certain high-end SCSI busses) then one of the drives can be swapped out and replaced without the server software realizing that anything untoward has happened.



    If you have two drives, they can be either striped or mirrored (for speed or reliability). If you have at least three, they can be both striped and mirrored, so that you get the best of both worlds, or you can stripe them for really high performance (this is what the performance junkies at <a href="http://www.macgurus.com/graphics/customraid.html"; target="_blank">Mac Gurus</a> do for a living).



    At the enterprise level, RAIDs can become truly enormous, climbing into the terabytes.
  • Reply 3 of 16
    [quote]Originally posted by Amorph:

    <strong>RAID stands for Redundant Array of Independent Drives</strong><hr></blockquote>



    Did they change the acronym? I always thought it was Redundant Array of Inexpensive Drives. Could be wrong.



    Wow, talk about nit-picking.
  • Reply 4 of 16
    [quote]Originally posted by spotbug:

    [QB]

    Did they change the acronym? I always thought it was Redundant Array of Inexpensive Drives.

    [QB]<hr></blockquote>

    Yes, you are correct. They changed "Inexpensive" to "Independent".
  • Reply 5 of 16
    cosmonutcosmonut Posts: 4,872member
    Is there a way to RAID two or more firewire drives? Would there be a benefit to this?
  • Reply 6 of 16
    eugeneeugene Posts: 8,254member
    It's weird since there is nothing redundant about RAID 0. It increases the likelihood of data loss by 2x.



    The most popular forms of RAID are:



    RAID 0: Data is striped across drives so that you can read/write off more than one drive. Your array will have the capacity of the sum of your drives.



    RAID 1: Data is mirrored across drives. Your array will have half the capacity as the sum of your drives



    RAID 0+1: Data is both mirrored and striped. Your array will have half the capacity as the sum of your drives



    RAID 5: Data and parity is striped so that data loss is unlikely. Disadvantages = not as fast as RAID 0+1. Advantages = much cheaper per capacity sought. Your array capacity will be the sum of your drives minus one drive.



    [ 02-14-2002: Message edited by: Eugene ]</p>
  • Reply 7 of 16
    And all this time I thought it was a bug spray

    boy was I off
  • Reply 8 of 16
    murbotmurbot Posts: 5,262member




    Me too Wrong Robot.



    <img src="confused.gif" border="0">
  • Reply 9 of 16
    It kills bugs dead.
  • Reply 10 of 16
    It kills dead bugs!

    thats not very efficant
  • Reply 11 of 16
    sebseb Posts: 676member
    Though I've never set up a RAID. I would presume you would need two drives of the same size and probably spindle speed.



    Right?
  • Reply 12 of 16
    theoretically you don't need two that are the exact same for striping, but it is recommened.



    i've got two raids of two 40 gig drives showing up as two 80's now. they're damn fast, and when transferring from my RAID to a friends, we can completely saturate 100baseT bandwidth.



    -alcimedes
  • Reply 13 of 16
    eugeneeugene Posts: 8,254member
    I forgot to mention. RAID 5 needs at least three drives.
  • Reply 14 of 16
    Since a striped array is not redundant, I've heard it called JBOD (just a bunch of disks).
  • Reply 15 of 16
    amorphamorph Posts: 7,112member
    [quote]Originally posted by CosmoNut:

    <strong>Is there a way to RAID two or more firewire drives?</strong><hr></blockquote>



    Yes. You can build RAIDs with any connection protocol. Solutions exist for SCSI, FireWire and ATA.



    [quote]<strong>Would there be a benefit to this?</strong><hr></blockquote>



    Yes. It's the most affordable way to set up a hot-swappable RAID, by a margin (hot-swappable SCSI is pricey). VST offers a FW RAID that supports up to 4 drives, and I know there's at least one other vendor out there who offers a similar product.



    [ 02-15-2002: Message edited by: Amorph ]</p>
  • Reply 16 of 16
    sdw2001sdw2001 Posts: 17,038member
    [quote]Originally posted by murbot:

    <strong>



    Me too Wrong Robot.



    :confused: </strong><hr></blockquote>





    I knew when I posted it was only a matter of time till this joke appeared. Thanks for the input though guys.....
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