RAID appearance

Posted on 2004-11-24
Last Modified: 2008-02-01
I have a powerful server with 3 hard disk (73 GB each) and a RAID 5 HW controller. OS is WIN2000 Server.

When I turn on the PC it shows 3 units (C,D, E) where C is 10GB, D is 0.2 GB and E is not formatted (though from BIOS i see it is 125.5 GB).

Is it correct ?
What am I supposed to do  if it is not ?
What should I see with a RAID 5 on, 3 logical units ? Should I see the space used for parity as space taken or not ?

Question by:minicuc
    LVL 32

    Expert Comment

    by:Luc Franken
    Hi minicuc,

    At this moment, you have a hardware RAID-5 array. Which will show up in windows as one physical disk.
    On that disk, three partitions are made.
    If you want to rearange the partitions, your best way will be to use disk management from within windows.
    Right-click "my computer" => "manage" => "Storage" => "Disk management"

    There you'll see the "1" disk. Graphically shown with the partitions on it.
    The only one you can re-arrange with disk management is the system partition (most likely C: in your case)
    If you don't use the 200MB partition at the moment (make sure it's not a recovery partition!!!) you might want to delete it.
    Then, create one big partition of the unallocated space (or whatever you like) and format it.
    Afterwards you should be fine.

    What your little mistake seems to be is that a RAID array doesn't show up as several different disks in windows (except in the device manager) but it shows up as one on which you can have 1 or more partitions.



    Author Comment

    Some more details:
    "Disk Management" shows:
    Disk 0: 10 GB, NTFS, Healthy (System), online, 3MB unallocated
    Disk 1: 196 MB, NTFS, Healthy (Pagefile), online
    Disk 2: 125.5 MB, Healthy, online

    Important info is that I have 3 SCSI hard disks,.
    So again, is it correct that I see these 3 units ?

    What should I see in My computer ? 3 units, right ?
    And in Disk Management ? one single disk, right ?

    So, since this is what exactly was delivered from producer, what do I need to do or did they do wrong ?
    Pls Be detailed as much as possible.
    Thanks a lot

    LVL 6

    Expert Comment

    The deffenition of raid 5 is:
    Independent data disks with distributed parity blocks.
    Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.

    RAID Level 5 requires a minimum of 3 drives to implement

    Since there is no striping and no mirroring, each disk is independent with only some space allocated for storing parity information. The only limitation is that information stored on a certien disk will have it`s parity info on another disk.
    Hope this helps.

    last note: Sizes are independent as well, there is no need for uniform size.
    LVL 6

    Expert Comment

    One more little thing,
    Disks in size of 73GB are always SCSI since IDE and standard SATA come in whole numbers.
    Just a little remark, sorry, just had to say it :)
    LVL 32

    Expert Comment

    by:Luc Franken
    >> Some more details:
    >>"Disk Management" shows:
    >>Disk 0: 10 GB, NTFS, Healthy (System), online, 3MB unallocated
    >>Disk 1: 196 MB, NTFS, Healthy (Pagefile), online
    >>Disk 2: 125.5 MB, Healthy, online
    >>Important info is that I have 3 SCSI hard disks,.
    >> Some more details:

    Is this a true RAID 5 array? If so, some should still be unallocated, or you've mistyped some numbers or mistyped MB/GB

    Disk 0: 10GB => is possible, but not with only 3MB unallocated, even if this would be a single disk, 63GB should be unallocated.
    Disk 1: 196 MB Pagefile => is possible if it's named Pagefile, but something should be unallocated if this is a true hardware RAID-5
    Disk 2: 125.5 MB =>I sure hope you meant GB

    >>Important info is that I have 3 SCSI hard disks,.
    >>So again, is it correct that I see these 3 units ?
    Nope, not correct in any way, it looks to me like something has been setup the right way, or you're reading something the right way. These readings are impossible.

    >>What should I see in My computer ? 3 units, right ?
    Not neccesery, like I said in my post above (http:#12667838) on a RAID array you can create as much partitions as you want. You should really think of a RAID array as one disk as that's exactly how it's interpreted to the system (in this case Windows) on which you can create partitions.

    >>And in Disk Management ? one single disk, right ?
    Yes, it should be listed as one disk.

    What kind of RAID controller do you have? And have you checked the RAID setup yet? What does the RAID setup mention about the RAID level running on your system, or does it at least mention the sizes of the individual disks?

    If you have the possibility, let the one that sold you this setup fix his work. This just doesn't make any sense to me.
    In case you want, I can show you a picture of my disk management and device manager to see what my setup looks like. (a RAID-1 array and a single disk on my home system, if I'm at my job, I can show you a picture of a RAID-5 array with three 36GB disks)

    LVL 32

    Expert Comment

    by:Luc Franken
    Or, maybe even better, can you upload a picture of your "disk management" and "device manager" (the last one sorted by connection)

    LVL 6

    Expert Comment

    Why one disk?
    They should be independent with only some unallocated space for the parity striping, no?
    LVL 32

    Expert Comment

    by:Luc Franken

    In a HARDWARE array, the controller card takes care of the whole array, the OS sees the ARRAY, not the independant disks (except when looking in the device manager on connected devices of course)
    If you're using a SOFTWARE array, the OS will have to manage all of the array, including the striping part and calculating the parity which will give a very high performance degradation as it'll has to use the main processor instead of what the controller card might be able to do for you (a RAID controller card has it's OWN processor to do all these calculations in real time without putting strain on the main processor)

    This is why a true HARDWARE RAID array will show up to a OS as just ONE disk. In fact, even things like defrag etc. are performed like it's just one disk.

    Unallocated means: "Not used" but in fact, the parity is a used piece of a RAID-5 array, a RAID-5 array of THREE 73 GB disks should show up as one disk of 146GB with all capacity available to use, the amount of storage used for parity won't show up in any way.

    I hope that makes it clear to you, feel free to ask for more information if needed.


    p.s. in this comment, all that is put in CAPS points out the relevant things (at least I think so :o) ) Not meant like shouting like the normal use of CAPS.
           General information about RAID can be found at (just click the RAID levels for info about them)

    Author Comment

    Right I meant 125 GB,
    It's a HP Smart Array 532.
    Further info displayed on HP configuration utility:
    Array A

    Author Comment

    Thx LucF
    Right, I meant 125GB.
    It is a Smart Array 532
    More details displayed from HP configuration utility:

    Array A:
    -Logical drive 1   10GB - RAID5
    -Logical drive 2   203MB - RAID5
    -Logical drive 3   125GB - RAID5

    Physical Drives attached toi port2:
    -SCSI ID 0  72.8GB
    -SCSI ID 1  72.8GB
    -SCSI ID 2  72.8GB

    All Physical Drives assigned: YES

    Number of Arrays=1
    Logical drives=3
    Physical Drives=3

    The server is a HP Proliant ML370G3 and I got it configured this way from producer.
    So maybe this is a standdard pre-configuration ?
    Do I have to configure the RAID myself ? in this case what should I do ?


    LVL 32

    Accepted Solution

    Thanks, that makes a whole lot more sense to me.

    >>Number of Arrays=1
    >>Logical drives=3
    >>Physical Drives=3
    This means nothing more than:
    Three disks make one array on which three partitions are defined. So in your case one of 10GB (for the OS), one of 203MB (for the pagefile, seems small to me, but ok) and one of 125GB (storage space)

    So, the RAID array is allready defined. 10GB+.2GB+125GB= 135.2 GB of available space. 72.8GBx2 = 145.6 (normal amount of overhead is the difference between these numbers)
    If you can't store files on the 125GB partition, it's probably not formatted yet, please go to Disk management as shown at http:#12667838 and right-click that partition to format it.


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