Assuming that the workload for the SQL Server is just a normal OLTP database, and that there are a total of 20 disks available, which configuration would make more sense?

A single RAID 1+0, containing all 20 disks. This physical volume would contain both the data files and the transaction log files, but two logical drives would be created from this RAID: one for the data files and one for the log files.

Or...

Two RAID 1+0s, each containing 10 disks. One physical volume would contain the data files, and the other would contain the log files.

The reason for this question is due to a disagreement between me (SQL Developer) and a co-worker (DBA).

For every configuration that I've done, or seen others do, the data files and transaction log files were separated at the physical level, and were placed on separate RAIDs.

However, my co-workers argument is that by placing all the disks into a single RAID 1+0, then any IO that is done by the server is potentially shared between all 20 disks, instead of just 10 disks in my suggested configuration.

Conceptually, his argument makes sense to me. Also, I've found some information from Microsoft that seems to supports his position.

http://technet.microsoft.com/en-us/library/cc966414.aspx

In the section titled "3. RAID10 Configuration", showing a configuration in which all 20 disks are allocated to a single RAID 1+0, it states:

In this scenario, the I/O parallelism can be used to its fullest by all partitions. Therefore, distribution of I/O workload is among 20 physical spindles instead of four at the partition level.

But... every other configuration I've seen suggests physically separating the data and log files onto separate RAIDs. Everything I've found here on Server Fault suggests the same.

I understand that a log files will be write heavy, and that data files will be a combination of reads and writes, but does this require that the files be placed onto separate RAIDs instead of a single RAID?