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Increasing Space on a Raid 5 configuration

Posted on 2003-03-13
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Last Modified: 2010-04-26
Hi,

The hardware we are using is:
Compaq ML370 Server
Compaq 431 Raid Controler
We replaced (not added) 9 gig drives with 36 gig drives.

Issue:
We replaced (not added) 9 gig drives with 36 gig drives.  So currently we have 3 36 gig drives using only 9 gigs worth of space (as would be expected).  We want to be able to utilize the rest of the space, but got worried that we were doing something wrong (seemed too good to be true).

To realize the extra space, is it as simple as using the array configuration utility?  Or what would be the best way to see all of the 36 gig drives?
Thanks,
Jay
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Question by:dpimcadmin
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11 Comments
 
LVL 9

Expert Comment

by:TooKoolKris
ID: 8129164
If you are using RAID 5 over 3 disks then your are going to loose 1/3 of your space due to parity information. You decrease the amount of space taken for parity if you increase the amount of disks in your array. For example if you were using 6 disks you would loose 1/6 for parity.

Hope This Helps,
TKK
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LVL 9

Expert Comment

by:TooKoolKris
ID: 8129174
This should be of some help as well.

HOW TO: Establish a Striped Volume with Parity (RAID-5) in Windows 2000
http://support.microsoft.com/default.aspx?scid=kb;en-us;303237

Hope This Helps,
TKK
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Author Comment

by:dpimcadmin
ID: 8129479
I understand the basics of raid 5 (3 disks - 2 usable) aspect, but what is the best way to see the new space if we replaced 3 9 gig drives with 3 36 gig drives, since initially the 36 gig drives will only show 9 gig usable.  What is the best way to expand?
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LVL 9

Expert Comment

by:TooKoolKris
ID: 8129550
If you changed the disks you need to rebuild the array from scratch. I assumed that you already had done that, my bad.
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Author Comment

by:dpimcadmin
ID: 8129627
And rebuilding the array will cause us to loose our data, right?  I was wishfull that we could just expand the current arry to take advantage of the new space.

Could we add a logical drive of the new space?

Thanks!
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Author Comment

by:dpimcadmin
ID: 8129662
And rebuilding the array will cause us to loose our data, right?  I was wishfull that we could just expand the current arry to take advantage of the new space.

Could we add a logical drive of the new space?

Thanks!
0
 

Author Comment

by:dpimcadmin
ID: 8129731
And rebuilding the array will cause us to loose our data, right?  I was wishfull that we could just expand the current arry to take advantage of the new space.

Could we add a logical drive of the new space?

Thanks!
0
 
LVL 9

Expert Comment

by:TooKoolKris
ID: 8129791
You could have simply expanded the array if you were adding disks that are exactly the same as those already in the array. You have placed an entirely new disk base in the array and this will require a rebuild of the array if you want to recognize the new space. Yes you will have to format these drives during the process but with proper backup you wont "loose" anything, except time anyway :)

TKK
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LVL 63

Accepted Solution

by:
SysExpert earned 750 total points
ID: 8130231
Depending on the RIAD controller, you may have another option.

1) Do a full backup of your data to tape on another server.

2) If your RAID controller supports dual RAID channels, then you can put the 9 GB drives back, check that the data is intact, and then just reconfigure the 2nd channel with the new 36 GB drives. You shoud get about 72 GB with 3 drives.

3) copy the data from the old drives to the new.

I hope this helps !
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LVL 9

Expert Comment

by:TooKoolKris
ID: 8130296
You will still new to build a new array to support the new disks no matter what you do.

TKK
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Expert Comment

by:avejue
ID: 8138684
With COMPAQ-RAID-Controller (depends on modell and firmware release), you have to start the array-config-utility and create a new logical drive one the free space of your raid. After that you can expand your current partition(s) or add new partitions. You have to use tools like Partition Magic or something like that for expanding.

One again: After you changed the last of the three 9Gig-HD's and the controller is recognizing the amount of space of all drive's (the smallest will dictate the new max. capacity - only for the case that there is any smaller one).

JA
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