[exim] RAID level for mailstore

Hi

I wonder what people think for a RAID level for their mail stores?

I can only have RAID 1 or RAID 5 and i dont have many users ~500 so what
do people think? This will be on a hardware RAID card but the RAID
channel will not be dedicated to the mail store ie there will be another
RAID disk sharing the channel.

Just want to lay the spindles out 'correctly'

thanks