I initially configured and set up a Windows 10 VM with a single core assigned to it, and now when trying to assign more than 1 core the VM crashes while booting. I have tried it with both host pass through and emulated CPU options. In the error log for the VM I see the following:

 

2017-01-07 03:59:33.132+0000: starting up libvirt version: 1.3.1, qemu version: 2.5.1, hostname: Tower

LC_ALL=C PATH=/bin:/sbin:/usr/bin:/usr/sbin HOME=/ QEMU_AUDIO_DRV=none /usr/local/sbin/qemu -name 'Gaming PC' -S -machine pc-i440fx-2.5,accel=kvm,usb=off,mem-merge=off -cpu host -drive file=/usr/share/qemu/ovmf-x64/OVMF_CODE-pure-efi.fd,if=pflash,format=raw,unit=0,readonly=on -drive file=/etc/libvirt/qemu/nvram/5ea6abc7-043f-d663-775c-ef3f2c5b2ffe_VARS-pure-efi.fd,if=pflash,format=raw,unit=1 -m 6144 -realtime mlock=on -smp 2,sockets=1,cores=2,threads=1 -uuid 5ea6abc7-043f-d663-775c-ef3f2c5b2ffe -nographic -no-user-config -nodefaults -chardev 'socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-Gaming PC/monitor.sock,server,nowait' -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime,driftfix=slew -global kvm-pit.lost_tick_policy=discard -no-hpet -no-shutdown -boot strict=on -device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x7.0x7 -device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x7 -device ich9-usb-uhci2,masterbus=usb.0,fevice virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0 -device vfio-pci,host=01:00.0,id=hostdev0,bus=pci.0,addr=0x4 -device vfio-pci,host=01:00.1,id=hostdev1,bus=pci.0,addr=0x5 -device usb-host,hostbus=1,hostaddr=6,id=hostdev2 -device usb-host,hostbus=1,hostaddr=2,id=hostdev3 -device usb-host,hostbus=1,hostaddr=7,id=hostdev4 -device usb-host,hostbus=1,hostaddr=3,id=hostdev5 -device usb-host,hostbus=1,hostaddr=4,id=hostdev6 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -msg timestamp=on

Domain id=2 is tainted: high-privileges

Domain id=2 is tainted: host-cpu

char device redirected to /dev/pts/0 (label charserial0)

 

(process:20930): GLib-ERROR **: gmem.c:100: failed to allocate 1048576 bytes

2017-01-07 04:00:03.854+0000: shutting down

 

 

 

I'm not sure what it is failing to allocate, causing the crash. Any insight would be appreciated.

I would guess that it's failing to allocate memory.  How much memory do you have installed and how much have you allocated to the VM

8GB installed, I've tried anywhere between 4-7GB dedicated to the VM. When leaving only CPU core0 selected it boots up without any issues, it's only when I add more cores that I run into an issue. I am running a Core i5 6600.

I'm just starting to learn about the whole VM subsystem, but I would think that the more cores you allocate to a VM the greater the overhead.  Just what the overhead is per VM per core, I can't at this point tell you.

 

But, I can say that with only 8GB of memory you are probably going to run into problems with a VM > 4GB (and 7GB is just going to be suicidal).  unRaid itself does require memory along with any plugins / docker apps etc that you might have installed outside of the VM

Adding another 8GB is on the to-do list, I guess I should get that done sooner rather than later. Thanks for the insight.