Recommended server specs

[cobuy]

Hello,

I'm thinking to deploy my first Proxmox instance.
Where may find recommendations regarding server specifications?
250Gb 64Gb for 1~4 VM is ok?

 

[Dunuin]

That really depends on your workload and what kind of storage you want to use. If you want ZFS as software raid for example you might want alot of RAM as by default ZFS will use 50% of your RAM for caching (and gets faster the more RAM you allow it to use).

A server for 4 VMs could be as small as 2 cores + 4GB RAM + 32 GB SDD or very big like TBs of RAM, 100+ cores and so on.
That totally depends on the VMs and the workload they are running....

 

[aaron]

as by default ZFS will use 50% of your RAM for caching

One should add, that this is "up to 50% if available" If it does not need it, it won't use it, as well as if other processes need it.

 

[Dunuin]

One should add, that this is "up to 50% if available" If it does not need it, it won't use it, as well as if other processes need it.

Yes, its best to manually set a fixed upper and lower size limit for ZFSs ARC that fits your needs. But you still might want more RAM if using ZFS instead of LVM to get good performance.

 

[cobuy]

Thank you for your reply.
In a first time it's for two VMs dedicated 20GB MySQL databases (one VM for each)
Our previous database server was on a 64Gb dedicated servers.
Then I guess if we didn't want to "downgrade" our DB appliance it would be safer to choose a 128GB server (?)

 

[Dunuin]

In general you don't want to overprovision your RAM. So if you really need the 64GB for each guest it would be better to use atleast 128Gb RAM. Also keep in mind that Proxmox needs a little bit of RAM and you always get a little bit of virtualization overhead. So with 128GB RAM it would be a little less than 64GB for each VM.

 

[cobuy]

Is there a way to assign dynamically RAM for VMs, or to priorize one of them ?

 

[aaron]

Is there a way to assign dynamically RAM for VMs, or to priorize one of them ?

Look at Memory Ballooning (needs drivers and service inside the VM) but as @Dunuin already mentioned, over provisioning resources can lead to problems if the over provisioned resources are all requested at the same time and don't forget, that Proxmox VE wants some memory for itself, the virtualization processes themselves also have some overhead additionally to the memory for the VM and depending on the storage you use, it wants some memory as well. Therefore, if you start to calculate memory that tightly, get more in the server!