No, by default MemTrimRate = "30", not "-1". Disabled memory page trimming sets this value to "0". I think "-1" has the same effect.
VMware Server uses a memory trimming technique to return unused virtual machine memory to the host machine for other uses. Although trimming usually has little impact on performance and might be needed in low memory situations, the I/O caused by memory trimming can sometimes interfere with disk-oriented workload performance in a guest.
To disable memory page trimming, check the Disable memory page trimming check box, and click OK.
Can I assume then that the trim rate values would be valid in between 0 and 30 too?
It sounds like a good thing to have happening, but performance is good too, so perhaps it'd be good to lower it instead of turning it off, if it's a rate?? Say, maybe to 10?
on my system it was set to -1. Having it set to that caused the VM to be unsable. Basically the disk I/O was so high that even simple navigation was difficult. By setting it to 0 the vm performs as expected