Logical disks/Disks array

Posted on 2006-04-15
Last Modified: 2010-04-03
can someone explain to me why this mismatch in size between the drives shown in the array controller and the windows  disk management, as detailed below?

MSA1000 Controller in 9522JN7L7CF
Array A
Logical Drive 1
(208930 MB,RAID 5)
Array B
Logical Drive 2 (560055 MB, RAID 5)
Array C
Logical Drive 3 (280023 MB, RAID 5)
Array D
Logical Drive 4 (858305 MB,RAID5)
Array E
Logical Drive 5 (34731 MB,RAID 1+0)
Array F
Logical Drive 6 (208390 MB,RAID 5)
Array G
Logical Drive 7 (8673 MB, RAID 1+0)

From windows Disk Management I can see:

Disk 0 show three partition
Disk 0            36 MB FAT    -  OS (C:)16.95 GB NTFS - New Volume 16.92 NTFS
33.91 GB

" I don't see Disk 1

DIsk 2                              User Data (H:)546.92 GB NTFS
546.92 GB

Disk 3                             Apps (I:) 273.45 GB NTFS
273.45 GB

Disk 4
838.18 GB                       Departments (M:) 838.18 GB NTFS

Disk 5                             Appro(K:) 33.91 GB NTFS
33.91 GB

Disk 6                             Profiles(P:) 203.50 GB NTFS  
203.50 GB

Disk 7                             new Name(N:) 8.46 GB NTFS
8.46 GB

Question by:jskfan
    LVL 4

    Accepted Solution

    This is not really a mismatch but only a convertion make look that way.
    For example is 1MB y 1000KB then you would not see any difference. but the real convertion is
    1MB is 1024KB such formula is used on GB the same way.

    So when it converts from KB to GB there will be a number difference but like said above is only to our eyes, they are the same after converting it back on forth.

    8673 MB / 1024KB = 8.46 GB

    Anything else post back.
    LVL 44

    Expert Comment

    RAID arrays span across several disks, and are not necessarily limited to a single disk.  SO a RAID 5 arry will extend across 3 disks, and give you a C volume approx. comparable to the size of all 3 disks combined.

    Assisted Solution

    There are various raid levels

    Raid 0 will is stripped disk (no fault tolerance) you will see approximatley the combined volume in all disks.
    example 2 100GB drives will give you a 200GB partition

    Raid 1 (mirrored) this gives you fault tolerance but half the space
    example 2 100GB drives gives you 1 100GB partition

    Raid 5 is also stripped disk but with fault tolerance so any 1 disk can fail without loss of data
    you need at least 3 disks. If more disks you will generally lose 1 disk in size.
    Example 3 100GB will give you 1 200GB partition.

    The Mismatch is in the raid. The controller will see all disks available and count bytes differently

    MS Disk Manager will only see the logical drive presented to it. You will not see each drive. You will only see the partition.

    I hope this explains it a little more

    LVL 9

    Assisted Solution

    CKWT is correct in that it's the 1024/1000 difference only. You asked this before and I didn't understand why you kept saying there was a mismatch. If that's all it was then get the other Q deleted and accept CKWT's answer for this one.

    Author Comment

    David_Fong ,

    I closed and rewarded points to the previous question almost similar to this. I still haven't gotten the answer I needed, though I have rewarded my points.

    well, can someone grab a disk size that shows on the array and tell me which want on the windows disk management is corresponding to, and why the difference is showing up?


    Array A
    Logical Drive 1
    (208930 MB,RAID 5)

    means 208930MB/1024KB=204.033203125 GB
    Where is the corresponding disk for 204.033203125 GB in windows disk management?


    Author Comment

    <<<<<Array A
    Logical Drive 1
    (208930 MB,RAID 5)
    means 208930MB/1024KB=204.033203125 GB
    Where is the corresponding disk for 204.033203125 GB in windows disk management?>>>>>>>>>>>>

    this is a cluster ,so on the other node I can see a drive that has 203.49GB this might correspond to 208930MB/1024KB.

    LVL 4

    Assisted Solution

    Can you see it on the explorer>My computer?

    Is that drive been worked on, pulled out, just installed, something occured that cause the windows information to outdate.

    Go into RUN>service.msc and restart logical disk manager and logical disk manager service... if this does not make the windows read your hardware list properly. consider rearranging the drives with there drive letters, swap some around...
    This is another way to force the hardware to be read again and maybe listed properly.

    If still dont work, You might have to consider running a MBR check. if the MBR has been modified by a GoBack service, or any other recovery tool that operates similar to Goback services, Windows manager may not show it or assing drive letters to it. to check it do this: boot from startup CD-ROM, choose repair option during setup, and run Recovery Console. When you are logged on, you can run FIXMBR. this is a last resort option.

    LVL 5

    Assisted Solution

    Simply, there are several ways of calculating capacity. One is technical, the other is marketing.

    I used to try to calculate in the past, and gave up because different systems do different calculations.
    I work a lot with Linux based servers where we for example install 4x250GB drives, the usable data (RAID5) after the drives are formatted with XFS is around 695GB and one would think it would be 750GB

    Hard drive vendors tend to market their drives as a 250 but you get 233 and so forth. Different systems use different methods of calculation
    LVL 9

    Expert Comment

    Looked at our backup server:

    ACU says      69452MB and 1680117MB
    Disk admin    67.82GB  and 1640.73GB

    Now 67.82GB = 69447MB, 1640.73GB = 1680107.52GB so in our case one of the disks actually appears larger in disk administrator than under the ACU and one appears slightly smaller.

    Only way to be absolutely sure which is which is to compare the LUN number under Array Diagnostic Utility with the properties in disk manager.

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