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Shutdown again you then need to set the min (current allocation) and max (maximum allocation) to properly use the vritio memory driver). You might want to watch your actual memory usage to determine best min because ballooning likely (need to check) take resources and you also want to not set yourself up to be over allocated if other systems ballon too. For my needs , Win 7 I find it usually stay stays at 1.6GB, so I allocate 1.6GB - 4GB.
Finally, the default realtek network should work, but to get better performance switch to the virtio network card and repeat.
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