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Raid 5 Question

Posted on 2004-09-24
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Last Modified: 2010-04-26
   We have a old dell server 1300 deminsion. It has 3 Quantum (roughly 8-9 gigs each) disks plugged into a scsi card. This is setup as a raid-5 array. Someone the other day jumped on the server and saw the C was 9 GIGs instead of 18. Any ideas why?
FYI, uses a Perc 2 driver.
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Question by:Fubyou
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Expert Comment

by:zerofield
ID: 12147288
I could tell you the formulas for raid, but for the sake of convenience, use this:

http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp


3 9 gig disks in a raid 5 would yield 18 gigs roughly.  if your C is 9 gigs, its either partitioned out of the available 18, or its not really in a 5 like you thought it was.
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by:Lee W, MVP
ID: 12147576
Are there other partitions?

Are you sure it's not a RAID 1 with Hot Spare?
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by:Fubyou
ID: 12148060
How could i tell if its raid 1 with hot spare
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Author Comment

by:Fubyou
ID: 12148062
Oh you mean mirroring
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Accepted Solution

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XSINUX earned 350 total points
ID: 12149706
Leew,  
              The Questionaire has only 3 Hard Discs. The minimum requirement for Raid 5 is 3 Hard Drives.  Hence there is no question of having a hotspare here.

Fubyou,
              Hotspares are standby Hard Drives that would be manually or Automatically configured to take up the working of a failed hard drive in a Raid Array. In you case, I suspect a Failed Hard Drive. See if the Raid 5 array is degraded. Try rebuilding the failed hard drive. If the Hard drive is offline, do not force it online as this might corrupt the entire array.

You should be seeing 18GB is all the hdd are working ( as the space contributed by one hard drive is in effective used for storing parity ) . Try and find out the failed hdd and replace it.

Note: If you have two 9 GB hdd and one 4.5 GB ( Total 3 )  hard drive in this Raid 5 Array, then the Raid would be using 3 hdds with the capacity of 4.5GB each ending up in a 9 GB Partition. This is because it configures the logical partition using the space of the least capacity hdd in the array. However the Wasted 4.5GB on the other two hdds ( 9GB Drives ) maybe cofigured to use a Mirrored Raid as your 2nd partition. This would result your D:\ Drive as 4.5Gb as effective space of 4.5 is used up to mirror the same. If your are using Raid 1 instead of the Raid 0 as your 2nd partition , then you would end up having 9GB as your D partition.

Hope this helps in someway.


Cheers
Sinu.
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