EFI VM's won't start under 7 Beta with Writeback Cache


Active Member
May 17, 2021
Oklahoma City, OK
Original Post Here

I can't get any virtual machines to start on 7.0-5 Beta when using writeback cache with Ceph backed raw virtual disks. The console hangs before the EFI stage begins. See attached image. At the advise of @t.lamprecht, I narrowed the problem down to the cache setting.

Won't Work:
scsi0: CephRBD:vm-111-disk-1,cache=writeback,discard=on,iothread=1,size=153601M,ssd=1

scsi0: CephRBD:vm-111-disk-1,cache=none,discard=on,iothread=1,size=153601M,ssd=1

Bug Report - https://bugzilla.proxmox.com/show_bug.cgi?id=3498


  • Screen Shot 2021-06-29 at 7.13.09 AM.png
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Hmm, cache setting can look like it would affect some behavior, but fully hanging seems a bit weird.

What was the longest time you waited to see if it wasn't fully frozen but real slow?

Also, did you try to use another display option than explicitly setting stdvga?

Just trying to see if there are some other factors playing (additionally) into that - thanks for your reports in any case!
What was the longest time you waited to see if it wasn't fully frozen but real slow?

Also, did you try to use another display option than explicitly setting stdvga?

I have waited several minutes between each iterative test. Tested using virto-gpu, VMware, and SPICE. No change. The results are the same. Graphics seems unrelated.

I also turned off SSD emulation, IO thread, and discard to test those settings. No effect.

What did work was changing the SCSI Controller. The LSI and MegaRAID controllers allow me to advanced past EFI settings. VirtIO and VMWare controllers hang with writeback cache. They work with caching = none.


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    Screen Shot 2021-06-29 at 10.35.35 AM.png
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That option needs to be a drive option (I adapted the release notes), e.g., in your case you'd do something like:

qm set VMID --scsi0 "CephRBD:vm-111-disk-1,cache=writeback,discard=on,iothread=1,size=153601M,ssd=1,aio=native"
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scsi0: CephRBD:vm-111-disk-1,cache=none,discard=on,iothread=1,size=153601M,ssd=1,aio=io_uring
scsi0: CephRBD:vm-111-disk-1,cache=none,discard=on,iothread=1,size=153601M,ssd=1,aio=native
scsi0: CephRBD:vm-111-disk-1,cache=writeback,discard=on,iothread=1,size=153601M,ssd=1,aio=threads

Won't Boot to EFI Init:
scsi0: CephRBD:vm-111-disk-1,cache=writeback,discard=on,iothread=1,size=153601M,ssd=1,aio=io_uring
Can you post your storage config (/etc/pve/storage.cfg)? Most importantly from that, do you use krbd for your "CephRBD" storage, and does it make a difference if you change it?
Can you post your storage config (/etc/pve/storage.cfg)? Most importantly from that, do you use krbd for your "CephRBD" storage, and does it make a difference if you change it?

Yes, I typically use the kernel RBD module for performance. If I use librbd instead (shutdown VM, uncheck KRBD, changed settings to writeback cache from none, boot VM) everything works as expected. The problem does not occur using librbd but appears to be isolated to the kernel RBD module when using the new io_uring. As tested above, the problem did not occur on KRBD when using aio=threads with writeback cache or when cache is set to none.

dir: local
path /var/lib/vz
content backup
prune-backups keep-all=1
shared 0

cephfs: CephFS
path /mnt/pve/CephFS
content vztmpl,iso
prune-backups keep-daily=7

rbd: CephRBD
content images,rootdir
krbd 1
pool CephRBD

pbs: PBS
datastore Home
content backup
fingerprint 0d:a2:fc:17:03:cc:50:83:00:cc:56:3d:24:69:b3:de:6d:ca:95:10:a1:9a:01:72:54:b0:09:e1:09:e3:c8:5d
prune-backups keep-all=1
username root@pam

proxmox-ve: 7.0-2 (running kernel: 5.11.22-1-pve)
pve-manager: 7.0-5 (running version: 7.0-5/cce9b25f)
pve-kernel-5.11: 7.0-3
pve-kernel-helper: 7.0-3
pve-kernel-5.11.22-1-pve: 5.11.22-1
pve-kernel-5.11.21-1-pve: 5.11.21-1
ceph: 16.2.4-pve1
ceph-fuse: 16.2.4-pve1
corosync: 3.1.2-pve2
criu: 3.15-1+pve-1
glusterfs-client: 9.2-1
ifupdown: not correctly installed
ifupdown2: 3.0.0-1+pve5 ksm-control-daemon: 1.4-1
libjs-extjs: 7.0.0-1
libknet1: 1.21-pve1
libproxmox-acme-perl: 1.1.0
libproxmox-backup-qemu0: 1.0.3-1
libpve-access-control: 7.0-3
libpve-apiclient-perl: 3.2-1
libpve-common-perl: 7.0-4
libpve-guest-common-perl: 4.0-2
libpve-http-server-perl: 4.0-2
libpve-storage-perl: 7.0-6
libqb0: 1.0.5-1
libspice-server1: 0.14.3-2.1
lvm2: 2.03.11-2.1
lxc-pve: 4.0.9-1
lxcfs: 4.0.8-pve1
novnc-pve: 1.2.0-3
proxmox-backup-client: 1.1.10-1
proxmox-backup-file-restore: 1.1.10-1
proxmox-mini-journalreader: 1.2-1
proxmox-widget-toolkit: 3.1-4
pve-cluster: 7.0-2
pve-container: 4.0-3
pve-docs: 7.0-3
pve-edk2-firmware: 3.20200531-1
pve-firewall: 4.2-2
pve-firmware: 3.2-4
pve-ha-manager: 3.2-2
pve-i18n: 2.3-1
pve-qemu-kvm: 6.0.0-2
pve-xtermjs: 4.12.0-1
qemu-server: 7.0-5
smartmontools: 7.2-pve2
spiceterm: 3.2-2
vncterm: 1.7-1
zfsutils-linux: 2.0.4-pve1

agent: 1,fstrim_cloned_disks=1
balloon: 0
bios: ovmf
cores: 28
cpu: host
cpuunits: 101
efidisk0: CephRBD:vm-111-disk-2,size=1M
machine: pc-q35-6.0
memory: 24576
name: encoder
net0: virtio=00:a0:98:7f:85:c8,bridge=vmbr1,firewall=1
numa: 1
ostype: win10
scsi0: CephRBD:vm-111-disk-1,cache=none,discard=on,iothread=1,size=153601M,ssd=1
scsihw: virtio-scsi-single
smbios1: uuid=3fe0d48d-0709-4e0c-99b6-8f8bcfb658f0
sockets: 2
tablet: 0
vga: std,memory=32
vmgenid: 1acdd3ec-cc43-4bcd-b739-05202257a5b2
vmstatestorage: CephRBD
Last edited:


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