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Expand Raid 5 array (3 x 36Gb) with a 72Gb disk

Posted on 2006-11-13
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We have a 72Gb disk that we would like to add to an existing Raid 5 array consisting of 3 disks of 36Gb, running on a Dell Poweredge 2600 with Perc 4/di with Windows 2003 Server. Array has 2 partitions - C: is 5Gb and D: is 67Gb (total of 72Gb). Here's what we plan on doing:

1) Backup the 2 partitions using Norton Ghost
2) Add the 72Gb, and reconfigure the array to expand using this new drive, for a total of 144Gb.
3) Restore the partition images with Ghost, enlarging at the same time the C: partition to 20Gb, and assigning the rest to D:

Question:
1) Does it matter if the added drive size is larger ? Will it add the full 72Gb of space to the Raid 5 array or will it only consider only 36Gb since the existing 3 drives are 36Gb

If we were not to use Ghost to restore the images:
2) Can we "expand" an array without loosing the data on the partitions on the array
3) Once the raid is expanded, could you modify the D: partition to use the new available space without having to recreate the partition (backup to ghost image, erase partition - recreate larger - restore ghost image to larger partition ) ?

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Question by:ndidomenico
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Pber earned 1000 total points
ID: 17930033
I'm not sure what Ghost will do, but here's what the array controller will do...

The array controller will only use 36GB of the 72GB disk.  All disks must be of equal size on an RAID set.  So you will only get about 100GB of space.
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by:QEMS
QEMS earned 1000 total points
ID: 17932073
We have done almost exactly that recently, added a 72GB SCSI disk to a RAID array which has only 36GB disks and as Pber pointed out, the RAID array will only use 36GB of the larger disk. This would effectively give you 3 x 36GB drives for data and 1 x 36GB drive for the parity drive.

It is advisible to backup all your data before doing anything like reconfiguring a RAID array, but ghost should not be necessary. It wouldn't hurt to take an image of the system but I'm not sure how things would go when restoring the ghost onto a different size array. In fact when we added the latest SCSI disk, the controller rebuilt the array, sorted all the data out and gave us an extra 36GB to allocate dynamically without any disruption to the existing data. Your server would have to be "out-of-action" for a few hours, so maybe its a good idea to let this happen overnight or at a time when your system could be down for the best part of a day.

I suppose the question now is - do you use dynamic disks? If so, you should be able to add the extra space to whichever drive you like with the exception of the system drive. If you do not use dynamic drives then you could look at converting your D drive to a dynamic volume (maybe look at this before you add the new disk), then you should be able to expand the partition without any data loss or problems.
To change the size of a system drive you would need other software such as Partition Magic. There are lots of options here (including some open source ones) but last time I checked there was no tool in Windows that would allow this. If you want good support with the process then its worth paying for a good piece of software, if your confident you could get everything restored from backups if it went wrong you could try an open source option first and resort to paying for a product if necessary.

Good luck with it =)
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by:ndidomenico
ID: 18047516
Thanks both for your help. I tested this on a test server and it formatted like you said (only half of the 72Gb used). Fortunately, I was wrong with the disk size in that server and they were all 72Gb! So the added 72Gb drive was used completely

Thanks
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