Proxmox: Do I need more memory? (long post)

[johnt]

Guys! I've done some crazy stuff with my servers. I used to be confined to Windows for work, but then I discovered Proxmox and it changed my life. I recently upgraded my system memory to 64 GB (up from 32 GB) and I'm surprised to see how much memory Proxmox likes to eat. The containers seem to be well behaved and use about as much as Proxmox reports - they are generally Ubuntu 24.10 LXC packages. It's crazy how much utility I can get out of a container running 2 CPUs and 2 GB of memory. SHEESH!

 

But my struggle are the VMs. I have one running Windows 11, which reports using about 3 to 4 GB of memory at idle within the VM, but Proxmox reports 15 GB of usage. I have provisioned 16 GB to the VM. I've scoured the internet and found Windows apparently lies about the memory usage in Task Manger. It's plausable!

 

But I have a second VM running Plex Media Server on Ubuntu Server (mainly because I need to passthrough the GPU for hw transcoding), with 8 GB provisioned. The guest OS reports around 1 GB used, but Proxmox reports 7 GB memory usage. I am not sure what to think about it lol This is all at idle.

 

Basically at an idle machine with a few programs running on the containers, my CPU is hovering at 3% while Proxmox says I am using 45% of memory.

 

I'm also planning on doing more with the server, including maybe adding a VM for TrueNAS or Unraid. Really haven't decided... but I'm worried if I go to TrueNAS I will probably want to use ZFS, and the rule of thumb for memory usage is going to kill me. I have about 40 TB of storage that would be on a single vdev, but I may consider buying similar drives and upgrading to like 4x24TB in RAID5 or similar config, so about 72 TB usable-ish storage. Not sure this would be a huge deal with Unraid.

 

I'm debating about adding 64 GB more memory. DDR4 is basically EOL and relatively affordable. Any thoughts? I'm running all this on an i5 12400. My CPU doesn't seem to be a bottleneck at this point, but I feel like I am going to run out of cores/CPU if I double my memory and continue growing.

[Electronics Wizardy]

The VMs typically try to use as much ram as they can at idle for caching. Turn on memory balloning to try to make that better. 

 

What is using that ram on the host? How much is ZFS? What does htop show?

 

How much ram do you have now?

 

I'd just use the ram now until you run into issues.

 

ZFS really doesn't need much ram, more is better as its used for caching, but thats the same with every modern OS now.

[Kilrah]

An OS always uses all the RAM it has available, if it's not in active use by processes it'll be used for caching (which is reported separately because it can be discarded at any time, not "lying").

So if your VM only actively uses 3-4GB of RAM and you want to run other concurrent things on the host give it 6-8, not 16. 

 

Containers are always preferred for minimizing resource use, dunno if there's a way to run Plex with HW accell on Prox/LXC but it's the common setup with Docker.

[LIGISTX]

Give the VM’s less RAM, and/or turn on ballooning. 
 

Your Ubuntu Plex VM will be fine with like 2GB of RAM… I have 128GB of RAM, and I only give my plex VM 2 or 3 GB, because it just doesn’t need more. Nothing it’s doing is RAM intensive. 
 

Similar with Windows. I don’t give my win 11 much, because it just doesn’t need much. 
 

I have an Ubuntu server VM for flight radar 24, and I think I give it like… 800mb? Don’t give VM’s more resources than they need. 

[johnt]

On 5/21/2025 at 9:35 PM, Electronics Wizardy said:

The VMs typically try to use as much ram as they can at idle for caching. Turn on memory balloning to try to make that better. 

 

What is using that ram on the host? How much is ZFS? What does htop show?

 

How much ram do you have now?

 

I'd just use the ram now until you run into issues.

 

ZFS really doesn't need much ram, more is better as its used for caching, but thats the same with every modern OS now.

I guess I'm not sure what they are caching. These are pretty fresh VMs with nothing on them. But what you are saying is consistent with what I've read. I don't have a zfs vdev yet. I guess my question, somewhere in there, was if I should get more memory in preparation for it... like 48 to 72 TB usable space. I have 64 GB now.

 

 

 

On 5/22/2025 at 12:52 AM, Kilrah said:

So if your VM only actively uses 3-4GB of RAM and you want to run other concurrent things on the host give it 6-8, not 16. 

 

On 5/22/2025 at 7:08 AM, LIGISTX said:

Similar with Windows. I don’t give my win 11 much, because it just doesn’t need much. 

I took your guys' advice and turned down my Windows 11 ram to 8 GB. Of course Proxmox is reporting nearly 100% usage, but I haven't noticed any slowness when using the VM over RDC. I don't really do a whole lot with it anyway. My overall memory usage, as reported by Proxmox, dropped to around 33% of 64 GB. That makes me worry a lot less.

 

 

 

On 5/22/2025 at 7:08 AM, LIGISTX said:

Your Ubuntu Plex VM will be fine with like 2GB of RAM… I have 128GB of RAM

What do you do with all that memory?? That's what I'm basically asking if I should upgrade to. It's a tough justification.

[Electronics Wizardy]

12 minutes ago, johnt said:

I guess I'm not sure what they are caching. These are pretty fresh VMs with nothing on them. But what you are saying is consistent with what I've read. I don't have a zfs vdev yet. I guess my question, somewhere in there, was if I should get more memory in preparation for it... like 48 to 72 TB usable space. I have 64 GB now.

 

There caching the disk. Might as well store as much disk as they can in ram to speed up disk IO typically.

 

If your not having issues with a lack of RAM I don't see a reason to upgrade. You can add a lot of storage with 64GB of RAM, so just keep using it till you have issues.

[LIGISTX]

6 hours ago, johnt said:

What do you do with all that memory?? That's what I'm basically asking if I should upgrade to. It's a tough justification.

I give 50GB to my TrueNAS VM. It doesn’t need it, I used to run the same TrueNAS system on 16GB… I have 10x4TB drives. But more RAM increases the ARC size, which makes it faster. Theoretically anyways. I mostly guarantee for my workload I could use 16GB and it would effectively be the same. But I wanted 128GB total so I can do practically anything I want with this server. I started with 64GB, but once I got to over a dozen VM’s, I figured for ~60 bucks more, might as well add another 64 GB. Used RAM on eBay is pretty cheap. Did I need it? No. But ¯\_(ツ)_/¯. 

[johnt]

7 hours ago, LIGISTX said:

over a dozen VM’s, I figured for ~60 bucks more, might as well add another 64 GB. Used RAM on eBay is pretty cheap. Did I need it? No. But ¯\_(ツ)_/¯

This is kinda the boat I am falling under. I'm just curious which CPU you are running for a dozen VMs? I feel like I have too much memory at 64 GB for my CPU (12400, 6 core).

[LIGISTX]

10 hours ago, johnt said:

This is kinda the boat I am falling under. I'm just curious which CPU you are running for a dozen VMs? I feel like I have too much memory at 64 GB for my CPU (12400, 6 core).

I used to run my homelab on an i3 6100..... your 12400 is plenty. 

 

I run truenas, half a dozen ubuntu server's, home assistant, about a dozen docker containers, and a a few LCX's. Something you are likley not realizing.... containers and headless VM's take next to 0 resources to run since they are doing quite litearlly, practically nothing. 

 

I am running a 28 thread Xeon with 8 threads turned off to *potentially* save a few watts of power, but my average CPU usage is like.... low single digits. Your 12400 with its 12 threads is likely at least 5x faster then my CPU, hell, it may be a full order of magnitude...

 

I just rebooted for some hardware maintenece, so the RAM has not fully filled up across all the VM's yet, but, trust me, your CPU is fine for a standard homelab type setup. I only went with this platofrm for the large amount of PCIe. I honestly should have gotten a less core count CPU, but at this point, 0 point in changing. Don't fix what aint broke type situation.