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Can you remove a disk from raid 5 without replacing it.

Posted on 2009-04-17
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One of our servers contains 3 72GB HDs and 3 146GBs hard drives configured as one RAID5 array. I need to install another drive. If possible I would like to replace one of the 72 GB hard drives with another 146 GB hard drive .Then I would like to remove the last 2 72 GB drives so that I can use the remaining 72GB of space on the 146 GB HDs, which up to this point has been unusable.
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Question by:MJcouture
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by:andyalder
ID: 24168098
Depends on the RAID controller whether you will be able to create another LUN on the extra space or not. What controller/server do you have.
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by:MJcouture
ID: 24168143
The server is an HP Proliant ML350 and the controler is an HP Smart Array 641 controler.
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by:chuckyh
ID: 24168253
"remove the last 2 72 GB drives" do you plan on replacing those with 146 GBs?
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by:andyalder
ID: 24168274
Yes, you can replace disks one by one and then go into the ACU and either extend the current logical disk or add another one. Check the rebuild process through the ACU so you don't take one out when another is still re-building. Option to extend logical disk is in right hand panewhen logical disk is selected.
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by:MJcouture
ID: 24168280
No, I would like to just remove the 72Gb drives one at a time and not replace them. That is why I asked if the RAID can be reuild on the remaing disks with out replacing the one that was removed.
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rindi earned 1000 total points
ID: 24168311
Usually you can't do that, as most raid controllers only allow you to expand your array with extra disks, and not reduce the number of disks. You'll have to replace the first disk, wait for it to finish syncing, then replace the next disk, wait or that to finish the sync, and then replace the 3rd HD and again wait until it has finished. Now as all disks are 146GB in size you should be able to use the smartarray controller's utility to expand the array to use all the disk space. Now that extra space should be visible in your OS as unformatted space, which can format as a new partition, or use builtin tools of your OS, or 3rd party tools to extend your already existing partitions.
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by:chuckyh
ID: 24168379
Do you plan on keeping it as a RAID 5 array? RAID 5 needs 3 disks minimum. If you just want to copy everything to the 146GB drive you can, but you wouldn't have a RAID 5 array anymore.  So the short answer to your original question is no.
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by:andyalder
andyalder earned 1000 total points
ID: 24168581
The controller can't reduce the number of disks in an array. You could replace the 146s with 72GB ones to get the bigger disks back to use elsewhere.
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by:Callandor
ID: 24170425
If you want to go from (3 x 72GB + 3 x 146GB) RAID 5 to (3 x 146GB) RAID 5, you'll have to back up the whole array, break the array, create a new 3 x 146 array, and then restore the backup to it.  You can't gradually reduce the disks by not replacing them.
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by:NetPro70
ID: 24174443
Make a complete backup or P2V-Migration (for desaster recovery). Remove one of the 72GB drives while the server is powered off. Then restart an boot OS. Add a new 146GB drive instead of the 72FB drive. Wait for the array rebuild process until it finishes. Process can be monitored on HP System Management Homepage. Power off server and repeat these steps for the next drives (only one at a time), until all 72GB drives are removed from the array. Finally after the array is consistent again boot from HP Firmware Maintenance CD (downloadable from HP support website) and make sure, all drives and controller have latest (cooperating) firmware. Update HP array configuration utility (assuming windows server) to latest version. You now can unse the new space on the array for new logical drives or even extend existing drives.
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by:andyalder
ID: 24174579
No, he wants to remove the 72GB disks and *not* replace them. It can't be done, has to backup/restore either the traditional way or by imaging.

BTW, you should not add the replacement disks with the server powered off in the swap one by one to increase size proceedure.
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by:NetPro70
ID: 24174697
@andyalder: I did not advise to add the replacement disk while the server is powered off! Just the disk to be replaced should be removed while the server is powered off because the removal of a drive which is not marked as failed by the controller is not supported at runtime. The new drive shall be inserted at runtime to be taken for rebuild without user interaction.
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by:andyalder
ID: 24174720
Oh you did, I misread. Sorry.
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Author Closing Comment

by:MJcouture
ID: 31571468
Thank you all for you input.
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