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I have a VMWare VM I have to use for certain tasks at work. For some reason while the VM is running or suspended something is doing massive (in terms of operations, not Bytes/s) I/O on its .vmem file, making the system on that disk very sluggish.

Resource Monitor basically shows the culprit of the performance problems:

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And the top spot in Disk Activity is always taken by the System process accessing said file.

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Anyone knows what's going on here?

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delayed writes? – Sathya Oct 30 '12 at 8:50
Half an hour after the VM was suspended? In packets of roughly 1 MiB/s? – Joey Oct 30 '12 at 9:22
just guessing, maybe VMWare's scheduling writes when idle or the like. Curious to know the real reason too – Sathya Oct 30 '12 at 9:37
I just tried whether it's the same after a restart, but got a Bluescreen when resuming the VM ... trying again now ;-) – Joey Oct 30 '12 at 9:46
Bit of background here on the suspended aspect. When you suspend a VM, it's RAM is written to the VMEM file. Watch resource monitor and you'll see a big block go from green (in use) to orange (modified) when you suspend the VM. Windows then flushes the modified blocks to the VMEM file. This flushing really hammers a SATA-3 drive causing a very unresponsive system. Second the modified memory hits zero, performance returns – munrobasher Mar 19 '15 at 0:40

According to vmware forums you need to have this setting in your config.ini: mainmem.useNamedFile = "FALSE" to avoid this problem. VMWare would use the real RAM and page file with this setting turned false.


share|improve this answer
This is more of a workaround than a fix - this problem appears to have got a lot worse in WS v11 on Windows 8.1. Suspect changes in memory management – munrobasher Mar 19 '15 at 0:38

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