As mentioned in an earlier post we have clients running SAP Finance applications. One of them is now going to upgrade to the latest version and because we host the application platform for them we will expand the infrastructure to hold the test environment and also upgrade from ESX3.5 to vSphere. As was the case last time we again have some anti-virtualization recommendations being done by the application consultants. As the solution is proven to work now for almost a year without fault (with an actual HA event no less) we fortunately have some leverage with regards to how we want to run the environment.
This time the discussion focuses on the use of RDM LUNs versus VMFS LUNs for hosting the SQL Server database files. Currently RDM’s are used mostly because earlier predictions were that the total DB size would near 1TB and we wanted to use SAN-based backup. In the mean time though there has been a switch to Veeam Backup & Replication for backup and DR purposes and that solution does not work with RDM LUNs. No problem as such but as we are preparing this upgrade/migration it is something to look at with regards to optimization. Also the size of the largest DB turned out to be about half the earlier prediction.
During my research on the subject I found it fortunate to have followed the VMware Design course recently as the subject of RDM vs. VMFS is a topic in the training. It was especially interesting to hear the differences on this topic related to what kind of SAN people were using/selling (NetApp, Equallogic, HP/Lefthand were mentioned most).
I also found some excellent papers and posts on the subject:
As soon as we have our final recommendation I’ll write another post explaining what we have chosen to recommend and why.