VMware’s Mac virtualization platform, Fusion, allows users to run in two different I/O modes. You can optimize for Virtual Machine Disk performance, or you can choose to optimize for other Mac applications running on the system. The second option uses unbuffered I/O so that Fusion takes up less memory on the system.
After finding that this exposed an underlying bug in the Mac OS X (10.5.x) which caused data corruption, VMware disabled this feature with its 1.1.1 release of Fusion. The feature was brought back in 1.1.3 for machines in which Mac OS X had been patched to 10.5.3 (where apple addressed this problem).
VMware now believes that 10.5.3 did not provide a complete fix to the problem after all and is urging Apple to “re-solve” this problem.
Hopefully we will have a resolution sometime soon. In the meantime, I will be running my fusion VM’s in buffered mode.
I know that historically, Apple has taken significantly longer than Microsoft to respond to known issues and vulnerabilities. Hopefully they will work with VMware to quickly resolve this issue!