Proxmox and VM sizing calculator
List the virtual machines you plan to run. See the CPU threads, memory and disk a Proxmox host needs, with room for the host, ZFS and growth.
7 virtual machines need a host with
Where the memory goes
- VMs 80 GB
- room to grow 20 GB
- ZFS cache 4 GB
- Proxmox itself 4 GB
- Total vCPU of the VMs
- 24
- Total VM memory
- 80 GB
- Total VM disks
- 1.14 TB
- Headroom included
- 25%
CPU can be shared between VMs (most sit idle most of the time), so 3 vCPU per host thread is assumed. Memory cannot be shared safely, so it is counted in full. Disks are counted as allocated; thin provisioning can stretch that, but plan for the full size.
Servers that fit
For a mixed set of VMs like this, a server with 16 threads, 128 GB of ECC memory and mirrored data-centre NVMe is a good start, for example the Ryzen 9 7950X3D. See Proxmox virtualisation servers.
The rules behind the numbers
- CPU is shared. Most virtual machines are idle most of the time, so hosts usually run 2 to 4 vCPU per physical thread. Choose 1:1 for VMs that are busy around the clock, such as build servers or game servers. Two threads are added for Proxmox itself.
- Memory is not shared. The calculator counts every VM's memory in full, plus 4 GB for Proxmox and, with ZFS, a cache (ARC) of 2 GB plus about 1 GB per TB of storage, between 4 and 16 GB. Recent Proxmox versions limit the ZFS cache to 10% of memory by default.
- Disks are counted as allocated, plus 64 GB for the host, ISO images and templates. Thin provisioning lets VMs share free space, but plan for the full size so a busy month cannot fill the pool.
- Room to grow is added to CPU, memory and disk, because new VMs always arrive sooner than planned.
For the servers that fit, the fast storage counted is the mirrored NVMe (RAID 1), the usual setup for VM disks. Storage servers also offer large hard disk pools for backups and bulk data.
Questions
How many VMs can I run on one dedicated server?
It depends on the VMs, which is why the calculator asks for them. As a guide, a 16-thread server with 128 GB of memory runs about 20 to 30 small Linux VMs (2 vCPU, 4 GB) at a 3:1 CPU ratio.
Can I overcommit memory?
Proxmox can balloon and share identical memory pages (KSM), but relying on it risks slowdowns and out-of-memory kills when VMs get busy. Size memory for the full allocation.
Should I use ZFS for Proxmox?
ZFS gives snapshots, replication and checksums, and it is the default for many Proxmox hosts. It needs memory for its cache, which the calculator includes when you tick the box.
Can I install Proxmox on a DediGermany server?
Yes. Proxmox VE is one of the operating systems you can choose when ordering, and you can add extra IPv4 addresses or a /29 subnet for your VMs.
Not sure which server fits?
Tell us what you want to run. We reply around the clock, usually within the hour.