I have been doing some reading on PVSCSI. We use FC enterprise class storage and from what I read it is the way to go for high I/O environments. And I understand that it is not supported with FT or for MS Clustering Services and that there is really no benefit when used in low I/O environments. My question is, besides the 2 ceavets listed, is there any reason why I would not use is for all new 2008 R2 VMs?
Just wanted to chime in that since PVSCSI was enhanced with vSphere 4.1 I have been using it in all server templates. I do not have any virtual MSCS clusters to worry about.
Matt Liebowitz has a great article on the topic that is worth a read: http://www.thelowercasew.com/more-vsphere-4-1-enhancements-welcome-back-pvscsi-driver
The test results show that PVSCSI is better than LSI Logic, except under one condition--the virtual machine is performing less than 2,000 IOPS and issuing greater than 4 outstanding I/Os. This issue is fixed in vSphere 4.1, so that the PVSCSI virtual adapter can be used with good performance, even under this condition.