Guidelines on Creating and Designing Database

Data and log files should be on separate physical drives so that, in case of a disaster, you have a better chance of recovering all data.
Transaction logs are best placed on a RAID-1 array because this has the fastest sequential write speed.
Data files are best placed on a RAID-5 array because they have faster read speed than other RAID-arrays.
If you have access to a RAID-10 array, you can place data and log files on it because it has all the advantages of RAID-1 and RAID-5.