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I'm replacing a Dell PowerEdge 2950 server (PERC 6/i) with a new PowerEdge R510 (PERC H700). The existing system has its system on a pair disks in RAID1. My intention is to re-use these disks on the new server, but I want to do a side-by-side migration of services.

My plan is to take one of disks across, repartition and install the OS. Once I have everything migrated and I can decommission the first machine, I intend to then move the second disk across and repair the RAID volume.

Obviously I understand the risks involved in this in that I will not have any redundancy during the migration, but I can live with that. What I just wanted to check is whether what I want to do is possible and whether there are any obvious pitfalls in what I am doing?

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Will the 2950 disks even fit in the 510? Didn't the form factor change from 3.5" to 2.5"? –  Mark Henderson Apr 26 '12 at 9:36
    
Did you purchase the R510 without hard drives? –  joeqwerty Apr 26 '12 at 10:30
    
@MarkHenderson: they're still 3.5" bays (you do have the option of buying 2.5" disks in 3.5" carriers) –  John Hall Apr 26 '12 at 10:38
    
@joeqwerty I'm buying the server with some drives but not all the ones I need. The two system drives in the original system will be redundant after the migration. –  John Hall Apr 26 '12 at 13:43

2 Answers 2

up vote 4 down vote accepted

It would work, but personally, I wouldn't do that with hardware RAID. There are too many implementations to deserve full trust in unsupported situations. It was not designed for that. It is a hack. Hacks have potential side effects. You won't know what can go wrong until it is too late. But I am sure there are lots of success stories too.

The biggest danger may simply be that the removed disk has an id saved somewhere, and if you add disks in the machine that have the same id, it might do something stupid. (For a software RAID example of this known issue, look at the difference between the ZFS file system's "zpool detach" and "zpool split". Split was created to support the type of thing you are doing. Detach is what you are thinking of doing.)

Do you even know for sure that the second system's RAID controller is compatible with the first one? If not, the disk won't work. (but the chance is high since it is a mirror)

If you used software raid (or hardware supporting 3 way mirrors), you could just add a 3rd disk to the mirror, and as long as you never move the disk back after removing it, you can't get any side effects on the original system. But it is still the wrong way to do it. If you clear out the MBR, superblock, etc. on those old disks and put them in the new system, the RAID controller might see some metadata you missed (unlikely, but who knows for sure?) and try to join it with the array and mess things up. Of course it 'should not', but you never know... this is not a supported situation. RAID was not designed for this, but other things were.

(based on your other question about windows domain servers, I'll assume this one is also about Windows)

On Linux, I would just copy the files (over the network, eSATA, USB, etc.) and reinstall the bootloader. Mac OSX has a tool that does it for you, as a supported feature. Unfortunately, I don't know the best answer on Windows, but you could try the built-in backup and restore feature instead. Or use some other backup software, or use specialized software for copying bootable systems.

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thanks for your caution. This is Windows and moving installations tends to be difficult. Also, it's a good chance for a clean start and an OS upgrade from Server 2008 to Server 2008 R2. –  John Hall Apr 26 '12 at 12:41

It should be perfectly possible to do that, but it's not an ideal scenario just because of the number of things that can go wrong. Ideally, I'd get a third disk, or storage system, to migrate my data onto and then move both disks over, but I appreciate that the resources might not be available to do that. I'd just make sure:

  1. You have a backup of your data!
  2. The PERC H700 is capable of growing a single-disk logical volume to a 2-disk RAID1 without wiping all the data
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make sure it is a perfect binary image backup as well.. –  dc5553 Apr 26 '12 at 9:41

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