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  1. #1
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    Question about RAID 0 on my Abit KG7 RAID

    Ok I have to quantum fireball SA 20.5 gigers installed on the Highpoint controller. I set them up to be RAID 0 Stripping. My understanding of this was that they would be identical and the computer would access the data faster becuase it could take half from one drive and half from the other. From what I can tell though it looks like my C: is now 41 gig. Did it just combine both drives under one letter or is my raid working correctly?

  2. #2
    Just Another Retired Moderator Jon's Avatar
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    When running a stripe set with two 20.5GB drives you will have one large disk with a size of 41GB. It uses both disks entirely when using RAID 0.

    RAID 1 will show you two separate disks...the main, bootable disk and the disk the mirror is going to so you relatively only have half the disk space available to you.

    In short, you're fine...don't worry.

  3. #3
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    help

    So how am I gettting increased speed if it just combines the two drives? Can you explain it?

  4. #4
    Just Another Retired Moderator Jon's Avatar
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    Say you have a 1 MB file and a RAID 0 setup. The RAID controller will take that 1 MB file and split it into (I'm going to use 64K as an example...4K, 16K and 32K could be used) 64K chunks which are striped SIMULTANEOUSLY across the two disks at the same time. This gives approcimately 75% faster read and write speeds since two hard drives are sharing the load of only one.

    It's very simple technology with a great result. 5 of 6 have RAID 0 in my home and they all would if I had the cash.

    Spanning a drive is what, I believe, you are thinking of. This is taking 2 or more drives and making one logical drive out of them. Only one disk is used at a time though in a linear fashion. When one disk fills up, the next is used and so on. RAID 0 writes half to one disk and half to another in equivalent stripes simultaneously so you have two mules for one job.

  5. #5
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    AHHH! Got it. I knew it was something like that. I thought it mirrored everything and just gabbed half the data from one drive and half the data from the other at the same time.

  6. #6
    Member theflyingrat's Avatar
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    Since only half the data is written on each drive, there is less waiting for the cylinders to rotate and the read/write head finding sectors. While one hard drive is searching for bits it needs, the other hard drive can already be sending them. AFAIK, the HDD controller will reassemble them for use by the CPU/memory/whatever. There is really a lot less waiting - plus, both drives are able to stream data at the same time.

    Assume this: one 20GB hard drive can put out, say, 20 MBps (an estimation). So if it wanted to read a 20MB file, it could take it a full second. If you're reading the same 20MB file off two separate disks, each containing half of the file, each drive will only have to read 10MB of data, roughly cutting the time in half (theoretically). Although real RAID isn't quite this efficient, some setups come pretty close.

    What you were thinking about is what's called mirroring. This would read and write the same data to two separate drives, and this type of RAID array (RAID 1), all 20MB need to be taken off each drive in order to get the file, resulting in it taking the full second. This configuration is for redundancy, not performance. It takes no longer or shorter to write/read info in this configuration.
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  7. #7
    Just Another Retired Moderator Jon's Avatar
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    Mirroring is RAID 1. You can also do a RAID 0+1.

    RAID 1 consists of at least two drives and whatever is written to the main drive is also written to the second drive...IN WHOLE. It just makes a mirror copy but perfromance is that of a single disk since only one disk is your actual active system disk.

    RAID 0+1 would be having a RAID 0 array and then another RAID 0 array that is a mirror of it. You get the speed of RAID and the redundancy of RAID 1. This takes at least 4 disks of equal stripe set. i.e. 2 X 20GB=40GB stripe + 2 X 20GB=40GB mirrored stripe.

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