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Thread: Raid 0 array - chunk size and allocation unit size

  1. #1
    Senior Amoeba iranu's Avatar
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    Raid 0 array - chunk size and allocation unit size

    Hi,

    Just set up my first RAID (0) array, hooray!

    I plan to partition the 320g (2x160) drive into

    1. OS Windows XP 15g (maybe overkill but my last install grew to 7g)
    2. Applications 30g (all those little things like winzip, mobo monitor etc, etc)
    3. Music/Video/DVD 75g
    4. Games 180g

    Before I start installing like crazy I would like to ask;

    I have set up the chunk size for the array at 32k. I read somewhere on hexus that this would benifit gaming. Is this correct or should I change before the installation bug hits?

    And during partitioning of the above drives, Windows XP asks for a "unit allocation size".

    What would be your recommendation for the above 4 drives; default, 16k, 32k, 64k 512k etc, etc?

    TIA

    btw

    I understand that chunk size is write 32k to disk 0, then 32k to disk 1, then 32k to disk 0 etc. i.e splitting data. Not sure which is best for what if you see what I mean.

    I understand the unit allocation size to be the size that windows writes data in, so a 128k program written to disk in an allocation size of 32k would be written in 4x32.

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    Quote Originally Posted by iranu
    What would be your recommendation for the above 4 drives; default, 16k, 32k, 64k 512k etc, etc?

    I understand the unit allocation size to be the size that windows writes data in, so a 128k program written to disk in an allocation size of 32k would be written in 4x32.
    I would recommend the smallest possible allocation unit, that is, 4K (Probably denoted by "Default" in this case). This may result in greater filesystem fragmentation, but anything larger prevents you from using NTFS compression.
    Also, unless you plan to work with large files, using a larger allocation unit would just waste space, in that smaller files probably won't fill entire clusters (A cluster can only be allocated to a single file - if that isn't the case, bad things happen. ). The average unused space in a cluster (Called cluster tips) can be roughly calculated: (Allocation unit size / 2) * number of files = Total wasted space.
    An interesting read on NTFS is over at http://www.ntfs.com/ntfs_optimization.htm

    Can't help you out with the RAID question, though. Sorry. :/

  3. #3
    dgr
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    here an idea for you though: if that array breaks, you lose EVERYTHING.

    at least create a 15gb partition on each drive and raid1 that - put windows and your docs on that, so if a hdd breaks, you don't lose anything.

    then raid0 the remainder of the space.

    sorted
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    HEXUS webmaster Steve's Avatar
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    Quote Originally Posted by dgr
    here an idea for you though: if that array breaks, you lose EVERYTHING.

    at least create a 15gb partition on each drive and raid1 that - put windows and your docs on that, so if a hdd breaks, you don't lose anything.

    then raid0 the remainder of the space.

    sorted
    Are you implying that he use dynamic disks to create a software RAID? That would not be wise.

    A non-RAID backup drive is a better idea IMHO.
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    dgr
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    dynamic disk? if you mean this:

    http://windows.about.com/library/glo...ynamicdisk.htm

    then he is clearly not using a dynamic disk, as he intends on partitioning it.

    and backups are simply that, backups. they aren't going to be up to date unless you rsync them every few minutes.
    dothan 745 @ 2.4ghz | 2gb Corsair XMS (2-3-3-6) | dual raptors (raid0) | ATI 9700pro | CM201 | dual lg 1810

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    Well I can't see how else you can RAID1 one partition and RAID0 the rest...
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    dgr
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    should be possible using a software raid system? AFAIK you should be able to do this at the partition level? Appologies if you can't.

    however its done, i'm just saying that your /home shouldn't be put on a raid 0 system - unless you want to lose it!
    dothan 745 @ 2.4ghz | 2gb Corsair XMS (2-3-3-6) | dual raptors (raid0) | ATI 9700pro | CM201 | dual lg 1810

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    As far as I'm aware, it can't be done through software RAID in windows without dynamic disks. In Linux it's possible, of course.
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    Senior Amoeba iranu's Avatar
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    Quote Originally Posted by dgr
    here an idea for you though: if that array breaks, you lose EVERYTHING.

    at least create a 15gb partition on each drive and raid1 that - put windows and your docs on that, so if a hdd breaks, you don't lose anything.

    then raid0 the remainder of the space.

    sorted
    I have thought of that!! I will back up any essential files including windows on a seperate 80gig standard ide drive.

    I will be using basic partitions as these are easier to ghost.

    At the moment my chunk size is 32k and unit allocation size is set to default so all should be ok. Thanks

  10. #10
    Senior Amoeba iranu's Avatar
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    Help!

    My raid 0 seems to be running fine. However, when I boot into windows xp I can't see the 80g ide ata 100 drive. I can see it in the Bios (1009) and I can see it in device manager with everything hunky dory BUT I can't see it in my computer or under disk manager, therefore I can't write to/from it.

    I have tried

    booting off disk 0 i.e. the raid disks
    changing all combinations of master/slave/ide 1/ide 2 etc

    I'm at a loss now anyone help?

    Athlon 2500xp
    Asus a7n8x-E deluxe
    Muskin 2x512 pc3200 level 1
    Radeon 9700 pro
    2 x 160g Hitachi Deskstars Raid 0
    1 x 80g WD (that can't be seen!!)
    Win xp SP1

  11. #11
    HEXUS webmaster Steve's Avatar
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    Have you initialised it in the disk manager...actually you won't be able to do that if you can't see it in the disk manager (doh.)

    Make sure you haven't disabled your IDE channels - check their properties in the device manager.
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    Senior Amoeba iranu's Avatar
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    D'OH with a large echo

    Just installed this drive into another PC and again it recognises it in Bios etc. However in disk manager its sees it as a "foreign disk". If you write click this there is an option to import the foreign disk, select this and bonza it works.

    I have now realised that I was seeing this before, however I was stupid (or not experienced enough - ahem) to think that the foreign drive was something to do with my raid array. lol

    Kez et al thanks for posting. I have increased your reputations.

  13. #13
    HEXUS webmaster Steve's Avatar
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    Iranu, worry not, I've seen a lot of people overlook that!
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