ASM LUN sizes and number of disks

Hi

We have a 200Gb database and there are 6X50gb luns comprising a diskgroup called dataDG

Since my database is growing around 100gb per year i am planning to add two 200Gb disks to the above diskgroups and simulatenously drop the 6 50gb disks off.

I understand reblance would trigger in my case and i am planning to add 200gb disks to the luns and increase the diskgroup sizes.

My question is there a formula or a rule of thumb to determine the number disks and the size given a database size and estimated growth rates?

regards
Hrishy       

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