|there is a big difference between raid5 and raid10. How many drives are used? Only 3? Then its raid5.|
Your question really pertains to your recovery plans. How will you recover the server if there is a problem?
Standard recommendation is mirror the OS and raid the data. This is two separate raid arrays. Your question pertains to a single raid volume.
Partitions on a single raid volume work but any disk space upgrade is a problem. For example lets say you want to add space to the c: [OS] partition. First hurtle depends on your raid controller. If it can dynamically restripe the array on the fly when you add drives you are OK. If not you have to reinstall from scratch. Lets say it can restripe on the fly. You end up with two partitions and available space. You can't span c: into this space. You have to delete the data partition, use server based partition manager software to expand c: into the raw region and then recreate the data partition and restore.
There are a number of other upgrade issues you can run into.
I know this really doesn't answer your question as to which is better, to partition or not to partition. Again it comes back to your recovery plan. How you will restore your server partially or completely will decide for you the issue of to partition OS from Data or not.