My 2c, start with 8 luns, and extend these as needed. Less work .....
Agreed unless you plan on exceeding 4TB then I'd go straight to 12 LUNs.
please explain how to do it best way .
It depends on the size of the DB and number of filesystems you have. If you use 500GB/filesystem as a rule of thumb, you can use that to determine if you need more filesystems or not. They should all be the same size too. For example:
up to 2 TB - 4 LUNs
up to 4 TB - 8 LUNs
up to 6 TB - 12 LUNs
Option 1 (if you need more DB directories):
add more DB directories (help extend dbspace). The downside of this method is that the DB will need to rebalance, so you will only get the performance benefits once the rebalance is complete. You get the space immediately.
Option 2 (if you have enough DB directories, but need space).
- extend all filesystems that the DB is using. The advantage of that method is that there is no need to rebalance the DB. But you can only use that method if you have enough DB directories already.