Migration of data from one SAN to another

[Anand Sreenivasan]

I have 6 HP boxes with dual adapters connected to SAN and they all use Powerlink for failover capabilities. Now, We want to move the data over to the NEW san. What I was thinking is to take one of the path down by just unplugging the cable and moving it over to the new SAN and then rediscover the devices and then migrate the data by either LVM mirroring or by using FCOPY and FRESTORE. My questions are 1) Am I right about unplugging the cable with out doing anything else in POWERLINK mode? 2) Is there any other option to move the data with minimal downtime?. Thanks in advance.

[Steven E. Protter]

Shalom Anand,

I think your path may work.

I think your path is dangerous and risks the data.

A better option is the old fashioned way. Back up the data to tape, or have both san's up and set up all the luns and let one of the connected OS's do the copy.

If by chance the two san's are compatible, there may be a supported way of connecting them and doing the equivalent of a business copy.

Full backup before you start, no matter what the decision is.

SEP

[Anand Sreenivasan]

Thanks Steve, But the problem is Business really don't like the downtime. I will have a backup before doing anything. I will have both SANS up and have LUNS assigned. And thats what I said about doing LVM mirroring. I will have both san disks in my system to do this...

[Ken Grabowski]

Anand,

Nothing will have you down longer than using a risky process and failing. You didn't say what kind of SAN you are using. If you have something like Continuous Access you can sync up the data between the two SAN's. Then have a short outage to swap out your luns.

I would hope you have a test environment that you can practice on in advance of the cut over.

[Sandman!]

Hi Anand,

If your new storage array is connected to the same fabric, then you don't have to unplug the cables on the back of your HBA. Simply zone the LUNs on the new array to your server(s) and then follow whichever migratory method you are using to move data off the old and onto the new.

[Scott Riley · Accepted solution]

Anand,

I just want to clarify, you said you are using "Powerlink" for path failover, do you mean pvlinks? I assume that is the case. I also assume by NEW SAN, you mean a completely separate fabric (if you are on a fabric that can see both arrays, by all means DONT pull one HBA, just zone your server to the new array, present the new LUNS then migrate).

Given those assumptions, I would:

1. Determine if an online LVM mirror is even possible. It is NOT possible if a) you LVM striped your lvols, b) your new LUNS are larger than the old LUNS and your max physical extents is too small for the new drives, c) you are adding enough drives to exceed Max PV's for the group, or d) the number of extents you are adding exceeds the maxium extents for the VG. If any of the above apply, you can't do an online mirror migration.

2. Perform a complete backup as you said.

3. Issue pvchange -s /dev/dsk/c#t#d# for every device. Force failover to the devices that will NOT be disconnected. Don't just pull the cable. Now is not the time to test that your other path is good. Issue the pvchanges, check for syslog errors, make sure everything is on the path that will remain up, all filesystems/devices are good, then and only then proceed :)

4. Pull the now unused path and connect it to the second fabric.

5. Present the new storage to the server

6. Perform the migration. If LVM mirroring is possible, do it, it works great.

If LVM Mirroring is not gonig to work, use a dd based copy. This requires you to create a new VG on the new disk, then copy the data between LVols while the filesystems are unmounted and the apps are down. The command I use is:

dd if=/dev/vg##/lvol## of=/dev/vgnew##/lvol## bs=256k

Run several of those in parallel. I have done hundreds of migrations this way, it works reliably and is usually much faster than the filesystem based backup/restore methods.

[Anand Sreenivasan]

I apologize, I should have been more clear when I am using the terms. Yes, It is a brand new SAN and I can't zone this with the existing array. I have to use the HBA's to discover the devices and use either the LVM mirroring or the Fcopy and now DD . Thanks a lot for the feedback, It is good to know that someone has done this before. I don't have that comfort of having a test environment. I have to make it work the first time and thats why I am checking with all you gurus. Appreciate all the feedback and I think I have a good game plan now to go about. Thanks again..

[Keith C. Patterson]

Anand,
Can you let us know how the migration went?
Anything to be aware of?

Thanks.