EV index volume size - best practice?

Hi,

I currently have two EV 11.0.1 exchange mailbox archiving servers archiving from two active exchange servers. Both EV servers have 300GB index volumes that are approaching capacity. They were originally 200GB each but were both extended to 300GB around 12 months ago.

My question is what is the maximum recommended size for an index volume? Should I go ahead and extend them to 500GB each (easiest option) or would there be more benefit performance-wise in creating new additional indexing volumes for each server and then set the current index locations to closed?

Are there any performance overheads for either option? The indexing volumes are currently hosted on a netapp filer.

Thanks

Paul