Understanding speed responsivness of Windows VM under VMM vs VirtualBox


I am a bit mystified understanding the speed responsiveness of Windows 10 VM on a DS920+.

NAS Configuration:

  • 20G RAM
  • 3 x 4T HDD in SHR
  • 1 x 512G SSD
  • NAS has 256G M.2 NVMe SSD Read only cache for both HDD and SSD

All Cases run the same Windows 10 VM, 8G RAM, accessed from Microsoft RDP

Case #1:

  • VM hosted under Synology VMM on HDD.
  • Quite slow to use, can’t do much with the VM.

Case #2:

  • VM hosted under Synology VMM on SDD.
  • A bit faster to use but still slow, usable for simple task if you are patient.

Case #3:

  • VM hosted under VirtualBox on a 2013 i7 iMac, the VDI disk is on the NAS HDD, cache is extensively used, network is 1G Ethernet.
  • Quite responsive, well usable.

Case #4:

  • Hosted under VirtualBox on a 2013 i7 iMac, the VDI disk is on local SSD.
  • A bit faster than Case #3 but not twice as fast.

I understand the CPU on the iMac is 2-3 faster than the CPU on the NAS, but is seams that the CPU speed has a bigger effect (even if the VM file is over the network) on VM responsiveness than the HDD vs SDD when running on the NAS under VMM.

Could it be that the implementation of VMM is inefficient compared to VirtualBox ?

I am quite surprised because running Windows 10 on a PC with HDD vs SSD has a huge impact. So how come running it on a HDD over the network does not make it impossible to run ?

Your thoughts are welcome.


I think if you change your M.2 NVMe SSD to read/write from “read only” you might be able to speed things up. Right now everything is getting written directly to the HDD and not temporarily stored on the SSD to be written when HDD/CPU is less busy. Also higher versions of Windows OS tend to use lots of memory so that can also have an impact.

Case #1 & #2
Check if you have vmm guest tools installed on the virtual machine. This allows you to change the hard drive driver from the default IDE to SATA or virtio.

Also check you performance mlnitor on the NAS under the RAM section if you see swapping. A value 》10% is an indication that you should add RAM.

Have at least 8GB of ram for the W10 machine and at least 2 cores. But do mot expect miracles. The DS920 was not designed for this workload.

Case #3 & #4
VM performance is all about latency. A single full or older SSD is not significantly faster than a RAID5 with read cache, especually with incresing file seize.

Thanks Stephan,
I already run VirtIO, the NAS has 20G of RAM so no swap, the W10 has 8G and run on 4 NAS CPU for the test. SSD is only 30% full, but it is not a super fast one.

I am wondering if having nVME Read/Write cache would improve over Read only cache.

But what mistified me is that the 1GbE network should be the slowest part when running the VM from VirtualBox on the Mac but it is still faster than running it from the NAS VMM on SSD.