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How do I migrate a RAID-5 to a single drive on Dell's PERC Array?

Posted on 2007-08-03
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I have a Dell PowerEdge server running SBS2000.  It uses a PERC 4/DI (PV22xS) SCSI RAID controller.  Currently, there are a total of 6 physical hard-disks.  2 are used in a RAID1 for the OS, 3 are used in a RAID5 for Exchange Server data, and 1 is a spare.  I would like to get rid of the RAID5 and replace it with a RAID1 instead, so that I can have a total of 2 spare drives; I also want to do this so that I can rotate disks out of the mirror and keep copies of the drives offline.  It seems logical that I should somehow mirror the RAID5 data to the single spare drive, and then kill the RAID5, and then make a RAID1 from the single drive.  However, I can not figure out how to do this.  I also can't add an IDE drive, nor can I use an external drive.  Since this is an E-mail server, I can not have significant down-time.  I need to be able to copy the data to the single drive so that when I reboot the system with the RAID5 removed, the system will work with the single drive.  How can I do this?
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Question by:judas2158
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by:SysExpert
SysExpert earned 800 total points
ID: 19627048
1) Remove the spare drive from your Rad configuration.

2) See if you have a 2nd SCSI board/ controller in the server. Most servers do.

3) Add in a large drive on the SCSI controller, and reboot.

4) Define the drive in windows, and start the copy process

then you can
change  the RAID 5 config to whatever you want.

I would also suggest doing a full tape backup of all partitions beforehand.

I hope this helps !
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by:judas2158
ID: 19627427
Well, there are only two backplanes and one controller.  3 drives on one backplane, and 3 on the other.  There is an integrated SCSI controller that isn't part of the RAID array, and I think it is SCA if I remember correctly, so it could probably drive the spare drive.  But I don't think that idea will work.  Part of the problem is in order to do the kind of copy you're talking about, I would have to unmount the exchange stores for the duration of the entire copy process.  I can only have a few minutes of downtime.  Even if I could copy the drive with the stores mounted, it would probably miss a few incoming emails as it went from mailbox to mailbox.  Exchange could be backed-up and then restored to the single drive, but if I did that, I would miss the handful of e-mails that come in past the backup point (during the restore operation), and I can't lose any e-mails.  That's why I was hoping to somehow build a mirror, where one drive is the single drive and the other drive is the virtual drive from the RAID5.  I don't think that can be done in that way, but there's just got to be a way for me to escape this RAID5 without missing any incoming e-mails.
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by:judas2158
ID: 19627452
Oh, BTW, the spare drive can be setup as an independent virtual drive within the array.  :)  The RAID5 can be transformed into a RAID0.  Is there a way to use that to my advantage?
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by:SysExpert
SysExpert earned 800 total points
ID: 19627687
You will not be able to do this in a short period of time.

You need to backup and restore the data, so that is the minimum amount of time the task will require.

There is no transparent method to convert RAID 5 to mirroring that I know of, but you can check the documentation anyway.

You might consider doing an image with Acronis Disk director onto the spare drive, redo the RAID, and restore. It may be quicker than an OS copy.

 
I hope this helps !
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raehrlich earned 1200 total points
ID: 19629295
You may want research mirroring at the OS level. Take your existing RAID 5 devices and mirror them to a new RAID 1. The OS's volume manager would copy the data in the background. When you are done, you can break the mirror and remove the RAID 5 devices. This assumes that you are migrating from a smaller to larger disk, or the exact same size, but not larger to smaller. Now there are a couple of things that could cause you problems. If this is a Windows box and you are migrating the boot/os drive you may need to manipulate the boot.ini file if the the scsi hardware path changes. In addition, if the geometry of the disks are different you may need to use diskprobe to manipulate it - diskprobe can be very dangerous if you don't truely understand what you are doing. Migrating the boot/os drive is always tricky. If you stick to moving just the data drives then you can be successful with OS mirroring, file coping with Robocopy, or backup/restore from tape.
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by:judas2158
ID: 19629781
Yep, all the physical drives are the same size, so the RAID5 is larger than the single drive.  The software RAID with the virtual disks was a good idea.  I thought about shrinking the partition so that I could do a partition copy, which might go faster.  I read some instructions about moving the database and streaming database locations for Exchange, and it made it sound as though the Exchange MMC would unmount and copy to the new location automatically, and then all I would have to do is remount it.  It still creates an interruption, but it sounds like it's easily reversible.  What I may have to do is mount another SCSI drive on the other controller, and do the software RAID with the RAID5 virtual disk and the new disk; it's a game of musical hard-drives, but I think it would work and keep me online 100%.  These are all good ideas and it did help me think things through, so I'll spread the points.  :)
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Expert Comment

by:MannageIT
ID: 31313225
do NOT take the software raid route.... way too slow and not totally fault tolerant.
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