Can I swap one RAID1 array for another in DL580 G4?

[Vague Assumption]

I've got a DL580G4 booting off a pair of 146GB's formed into a RAID1 drive.

I need to test out whether the server will run W2K12 R2.

If I pop in another pair of virgin drives and load W2K12 R2 on them AND it all doesn't go well,

do you think I can just pop the original RAID drives in and return to status quo?

Do you think W2K12 R2 will run on the server at all?  It has four 3.20 GHz XEONs?

[Jimmy Vance · Accepted solution]

if the RAID set is healthy and you properly shut down the system and then remove the drives attached to the RAID controller, you shouldn't have any issues with installing a different drive(s) to try an installation. When your done testing shut the system down and you can then put your original disks back in the system.

[Vague Assumption]

Thanks for your quick response.  

When I wrote to you, I was planning to perform a preliminary test on the server, to see whether the array  would behave as you said.

My further question is:  to do the test I'll outline below, will I need to restart the server to make the dry run reflect what will happen when I, should I, revert back from the array containing W2K12R2 to the W2K8R2 array ?  They're very stingy with windows, and I've already used one to check the BIOS revision level (P59, 9/28/2006)

Here's the test:  the server has, in addition to the boot RAID 1 array, a separate RAID1 array that supports a W2K8 page file.   This RAID1 array resides in the server chassis itself, and is powered by the same controller as the boot array.    In order to test the boot array's behavior, I wanted to

1.  Disable the page file.

2.  Hot-Remove the Drives

3.  Hot-Add a new pair of drives, complete virgins, no volumes, factory fresh.

4.  Run HP ACU to see whether the system accepted the array -- that I DIDN'T need to create a new array; and that I received no pop up warnings that something had gone wrong.

5.  Presuming that array remained in place, format the drives, using the same drive letter that the original page-file array had been assigned.

6.  Copy some files to them and from them.

7.  Hot Remove them.

8.  Hot insert the old array.

9.  Check the HP ACU to see whether the array was still intact

10.  Copy files to and from the array

11.  Re-create a page file.

To be  brief, is this a fair test, or is the proper operation of the re-inserted, previously existing array contingent on their being a cold restart between the use of the different arrays?   May I ask you to speculate what would happen at each step of the proposed process?

I was concerned that the controller would recognize the original disks, when reinserted in step 8 as not belonging to the  array that had most recently contained the substitute drives.

Is the array conscious of the drives identities?  Does it write on them a signature that correlates drive to array?  After all, if you accidentally switch positions of the drives in a boot array after working on a machine, doesn't it  tell you that there has been a reversal in the drive positions?

[Jimmy Vance]

You can't hot swap a working mirror set an expect all the data to remain intact. When you plug in the new drives, they will not have any raid configuration so you won't be able to access them until you create an array.

The controller itself doesn't store the array information, it is stored on each disk. If your shutoff the server and move the drives around the controller will spit out a message during POSt that the drive positions have changed and update the configuration. This was not always the case, older Smart Array controllers do not support this feature

[Vague Assumption]

Thanks for the concise and prompt response.  This one goes in my binder of server knowledge!

[Vague Assumption]

So, even if I had a pair of disks which had been in an array in the server previously, I stll could not hot swap them in?

[Jimmy Vance]

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@Vague Assumption wrote:

So, even if I had a pair of disks which had been in an array in the server previously, I stll could not hot swap them in?

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My first thought would be no, but I don't think I've actually tried that scenario. Even if the cortroller recognised the drives as a RAID set, I doubt it would be healthy and would need to rebuild.

Anytime you want to retain a RAID set you should power the system down so everything is in sync and then remove or install the disks

[Vague Assumption]

While we're on the topic, I thought of another thing that I could trip over.  I'm building the new server on a pair of 600GB 2.5" SAS drives.   If I need to turn the server off, and reinsert the array that originally drove, will it accept an array of a smaller size?

Maybe it will, since all the datra about the array is on the drives.

:)

Thanks in advance.

[Vague Assumption]

I ended up doing exactly that:  shutting the machine down and putting in the other drive set. 

The thing I did learn here is that the system won't detect any array on the drive mirror pair -

-- and the right way to handle this is to create the array.

You might have thought that creating the array would destroy the data on the disks, but it doesn't: it just loads the metadata about the array from the disks into controller memory.  When it's finished, the server can be booted to the personality it had before the 'newer' 'experimental' drives were added.