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RAID: Can you rebuild to a smaller drive providing capacity is still ok

Posted on 2013-01-24
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Last Modified: 2016-11-23
Dear All,

Quick question as not been in this scenario before with this particular type of kit.

Client needs to pull drives from a server and wants to put lesser sized disks in there.

I.e. 2x 600GB SAS drives.

They can offload the data and be left with the servers themselves and have only 100GB in use.

Proposing:

Server
a) 600GB SAS
b) 600GB SAS
In RAID 1 mirror

Replace Drive B

Server
a) 600GB SAS
b) 146GB SAS REBUILDING
In RAID 1 mirror

Let it rebuild ... Then swap over Drive A

Server
a) 146GB SAS REBUILDING
b) 146GB SAS

So then you are left with a server with same config, lesser drives, then drives can be reused in larger array elsewhere (naturally being wiped).

They need to do a couple of servers in this manner. O/S is Windows 2003 SP2 (not that this matters really). Cards are PERC 5/IR in RAID 1.

BTW - These are Dell PE 840 servers so NOT hot swappable drives but internals.. So server off and swap jobby.... But thats not a problem

In theory all this is ok providing capacity used is less or will it fail as capacity is different when Drive B is inserted and it auto starts to rebuild?

Thanks all..

R
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Question by:Romolo
7 Comments
 
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Accepted Solution

by:
Paul MacDonald earned 668 total points
ID: 38814342
No, at least not with any RAID technology I know of.

What you can do is build a smaller RAID, and then copy all the data over from the larger one.
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Assisted Solution

by:kdshipss
kdshipss earned 668 total points
ID: 38814395
The sizes are not the same and might create problems for you. Since it's not hot swappable, you still need to shutdown anyway. I would recommend that you create a backup of the current system state and data, and then rebuild the server with the 146GB drives on RAID 1, and then restore the system state and data. Ensure the size of the backed up data is not larger than the available free space on the newly built RAID 1. Do this at less busy hours and you will be fine.
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Assisted Solution

by:David
David earned 664 total points
ID: 38814463
No.  The reason is that the controller has no idea how much of that 600GB is in use.  It sees 1s and 0s.  It is not aware of file systems.  If it was built for a 600GB volume, then it needs a replacement drive >= 600GB.

BUT ... if you back up NOW, and make 2 copies for safety and make 100% the copies are good and you can restore on another system ..

Then you are free to blow away the config entirely and use the 600+146GB drives and build a new 146GB RAID1.  Then restore.  Problem solved.
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LVL 7

Author Comment

by:Romolo
ID: 38814666
Yup... That was my default answer. Backup... new volume... restore.

However, they REALLY wanted an answer to the above proposal.

Thanks all ... as I thought it will be a no no, however, was not nearly 100%..
Thanks again.

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Expert Comment

by:ajs21
ID: 38814695
not possible.  backup, move data, create new Raid-vol, restore.  best approach.
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LVL 47

Expert Comment

by:David
ID: 38814698
well at least now you can tell them why it can't work instead of just saying it won't work.  That should take the option off the table forever.
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Author Closing Comment

by:Romolo
ID: 38826540
Thanks everyone..

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