Slow write performance on SATA controller passthrough

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I have Proxmox 5.1. Xpenology 1.02b loader;  DSM6.1.4 Update 5.    Intel onbard (AHCI) SATA controller passthrough.  I have 3 SSD in RAID0 mode.  What I notice is, the write performance on SSD is terrible.  I've try to tweak Proxmox, and the Xpeno VM, but nothing seems to help.   


My VM config:

args: -device 'piix3-usb-uhci,addr=0x18' -drive 'id=synoboot,file=/var/lib/vz/images/100/synoboot_jun2b_virtIO.img,if=none,format=raw' -device 'usb-storage,id=synoboot,drive=synoboot'
bios: ovmf
boot: 4
cores: 4
hostpci0: 00:17.0,pcie=1
machine: q35
memory: 6144
name: DSM6.x
net0: virtio=00:11:32:xxxxxxx,bridge=vmbr0
net1: virtio=00:11:32:xxxxxxx,bridge=vmbr1
numa: 1
ostype: l26
scsihw: virtio-scsi-pci
serial0: socket
smbios1: uuid=7fda6843-8411-473f-91a5-xxxxxxxxx
sockets: 1


I've tried  to passthrough the VM without q35 machine type, and without PCE=1. Write performance is the same.     


hostpci0: 00:17.0


What's strange is, the write performance was really good back in October, when I was still on Proxmox 5.0.      So I want to ask everyone, how's your SATA passthrough performance? 

Screen Shot 2018-01-02 at 10.24.13 AM.png

Screen Shot 2018-01-02 at 10.25.29 AM.png

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glad to hear your problem is solved. would you share your synoboot_jun2b_virtIO.img ? i suppose you have embedded virtio and virtio-scsi driver? it will be great if you can share the template. thanks in advance!

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guess i solved my own problem, just follow the tutorial in this forum, and don't set CPU as host, set it to kvm64 as instructed, and everything will work.

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