Oracle 10g Storage Migration We need to migrate the storage of our production database. What is the appropriate method of doing so and what specific/generic precautions do we need to take??

Database Configuration:
Volume Manager - ASM using Raw Disks. ASM External Redundancy as storage is published from storage subsystemDatabase version - Oracle 10g R2Database Size - 5TB approx.

Existing Storage (source): HP MSA 2312sa Dual Controller. Directly connected to our database server (no fc or ethernet switch).
The Oracle binaries are also on this storage

New Storage (Target): HP EVA6300 FC storage. This storage will be connected to the hosts via FC switches.

Can we use host based storage migration like VxVM Plex attach/dettach to copy data from source LUNs to the target LUNs?
Do we have to use Oracle RMAN backup and recovery method for storage migration?
There is no need to copy the files - there is an ASM "trick" that does exactly what you want to do with no interruption in service. When ASM rebalances a disk, it maintains a list of viable LUNS for each block independently of the LUN on which it presently lives. It also won't drop a disk on which there are active blocks without rebalancing elsewhere - but it will mark it as not a viable home for rebalancing!

Once you have used oracleasm to make the new LUNs visible to ASM, you just issue the single command (forgive syntax, off the top of my head)

alter diskgroup my_dg add disk 'new1', 'new2', 'new3' drop disk old1, old2, old3;

Then sit back and wait. ASM will hot-relocate each block from the old storage to the new, laying them out nicely on the way, and drop the old disks when the operation completes. I/O will be a bit higher, but your users probably won't notice a thing.

As for your ORACLE_HOME, I'm afraid switching that will require a (brief) outage.