my gut feeling is that you wont have to recreate your HACMP configuration.

However, in terms of design your disks are a SPOF.

If I were you I would be looking at putting both disks in a RAID 0 config - as you have only two disks - as the DS4300 level, and then creating LUNs that are RAID backed. Once you get the LUNs, 1 in each volumn group you will have an identical HACMP config, but you will have some redundancy in your external storage.

I would not use LVM mirroring as redunancy - because both copies might end up coming from the same physical disk. And DS4300 RAID should give better performance than LVM mirroring.

As you asked for suggestions - I would backup to something else, create a LUNs on a RAID configuration of external storage - one LUN per volumn group - restore data, and restart application under HACMP.

I dont see how you are going to avoid some downtime - unless you can fit the application on internal storage, and run without HACMP, while you recreate the LUNs.

And, IMHO, you are very correct in your feeling that the config as it is now it far from ideal.