I have 3 instances of SQL Server 2008, each on different machines with multiple databases on each instance. I have 2 separate LUNS on my SAN for MDF and LDF files. The NDX and TempDB files run on the local drive on each machine. Is it O.K. for the 3 instances to share a same volume for the data files and another volume for the log files?
I don't have thin provisioning on the SAN so I would like to not constaint disk space creating multiple volumes because I was adviced that I should create a volume (drive letter) for each instance, if not for each database. I am aware that I should split my logs and data files at least. No instance would share the actual database files, just the space on drive.
Keep in mind, database disk configuration depends heavily upon your use cases. Therefore, for your environment, you may get perfectly acceptable performance by using only a log LUN and a data LUN. The key is to have data and log separated, as that will reduce IO contention.
Past that, you may wish to separate one or more instances off to separate drives if they have IO use that impedes another instance from operating at the desired performance.
Conversely, keeping all instances on the same drives may increase performance if individual instances rarely max out IO, and you have a small number of spindles.