for certain application best practice they would prefer to bypass vmdk and have access to the disk. i would just follow afterall the application know best for their app. raw disk mapping to the raw LUN would do. http://vmzare.wordpress.com/2007/02/19/vmware-raw-device-mappingrdm/
Different virtual storage controller can give multiple queues.
I suggest to use the PVSCI controller for better performance and check that guest OS partitions are aligned:
About RDM the diffence is not so high, so I suggest to do not use them:
Thanks Guys. No, I don't see any benefit in going RDM and I don't honestly think the I/O will be high enough for PVSCSI. Even though the SAP guys suggested, yy search so far has not brought forth anything to indicate that multiple virtual adapters are good or bad or neither here nor there. For simplicity I think we will just stick with a single adapter. We're not using SAP, but a similar database app, but again the vendor for that app had no specific recommendations either. Cheers.
If anyone else picks this up and has input, feel free to respond.
This link is a good place to start http://www.vmware.com/solutions/business-critical-apps/index.html
The only thing that will be truely relevant will be your testing in your environment based on your actual or expected loads. Luckily virtualization makes it practical to test many different configurations.
I am not sure, why you are hesitant to use Multiple SCAI Adapters. Right now, I donn't remember where I read this, but having different SCSI adapters for your OS and Application (heavily used) always helps.
I am not a big fan of RDM, it has caused lots of problems for me in the past but still I am using it in my environment.
The reason is that multiple controller means multiple queue.
IMHO I do not use use one controller for each disk, but for example I prefer keep the OS disk with a "standard" controller and data disk with PVSCI (with a queue increased).
But it's just a fine tuning... you cannot expect a 2x increase of perfermance