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VM Best Practices in Proxmox VE

Recommended settings for creating new VMs on Proxmox VE 9.x with modern guest operating systems.

Machine & BIOS

Setting	Value
Machine Type	`q35`
BIOS	`OVMF (UEFI)`

q35 is the modern chipset model, enabling PCIe devices, Secure Boot and better hardware emulation
OVMF replaces the legacy SeaBIOS
Important: Set the BIOS type before installation — changing it afterwards will make the VM unbootable
Confirm the auto-created EFI disk when prompted

Disk

Setting	Value	Notes
Bus/Device	`SCSI`
Controller	`VirtIO SCSI single`	Required for IO Thread support
Discard	✅ enabled	Enables TRIM/UNMAP — allows thin-provisioned storage (ZFS, LVM-thin, Ceph) to actually reclaim free space
SSD Emulation	✅ enabled	Signals to the guest OS that the device behaves like an SSD; especially useful for Windows guests
IO Thread	✅ enabled	Better I/O performance
Cache	`Default (no cache)`	Safe default. `Write back` gives more performance but risks data loss on power failure
Skip Replication	❌ disabled	Leave off — only relevant for ZFS-based Proxmox replication jobs, meaningless on Ceph

Async IO (for Ceph/RBD)

Mode	Description	Recommendation
`threads`	Legacy thread pool, synchronous syscalls	❌ Outdated, worst performance
`io_uring`	Modern Linux interface, PVE default	✅ Good for ZFS, NFS, thin-LVM
`native`	Linux AIO (posix_aio), O_DIRECT	✅ Best choice for Ceph/RBD, iSCSI, NVMe

aio=native requires disk cache to be set to Default (no cache). This is already the standard for Ceph, so no extra steps needed.

Network

Setting	Value
Model	`VirtIO (paravirtualized)`

VirtIO delivers the highest network performance of all available models.

CPU

CPU Type	Compatibility	Additional Flags
`x86-64-v2-AES`	Intel ≥ Westmere, AMD ≥ Opteron_G4 (~2010)	`+aes`
`x86-64-v3`	Intel ≥ Haswell, AMD ≥ EPYC (~2015)	`+avx, +avx2, +bmi1, +bmi2, +fma, +xsave`
`host`	Identical hardware only	All host CPU features

x86-64-v2-AES is the Proxmox default — safest for mixed clusters with different CPU generations
x86-64-v3 is recommended if all hosts support it (most CPUs ≥ 2015 do) — notable gains in compression, cryptography and modern workloads via AVX2
host gives maximum performance but prevents live migration between different CPU models

Recommendation:

Homogeneous cluster or single node → x86-64-v3 or host
Mixed cluster with different CPU generations → x86-64-v2-AES

Memory

Setting	Value
Allow KSM	✅ enabled (default)

KSM (Kernel Samepage Merging) allows the host kernel to deduplicate identical memory pages across VMs, saving RAM when running multiple similar guests.

Safe to leave enabled on self-managed clusters where you control all VMs
Disable for individual sensitive VMs if needed: qm set <vmid> –allow-ksm 0
Only disable globally on hosting environments with untrusted tenant VMs (side-channel risk)

Quick Reference

Component	Setting
Machine	`q35`
BIOS	`OVMF (UEFI)`
SCSI Controller	`VirtIO SCSI single`
Discard	✅
SSD Emulation	✅
IO Thread	✅
Cache	`Default (no cache)`
Async IO (Ceph)	`native`
Skip Replication	❌
Network	`VirtIO`
CPU Type	`x86-64-v3` (homogeneous) / `x86-64-v2-AES` (mixed)
Allow KSM	✅

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