VM guest using more resource RAM than its allocation.

[nwongrat]

Is it possible that VM guest using more resource RAM than its allocation.?

I am running 2 VMs. Each VM has no fancy setting. It just straight forward setting via web GUI.

This node has 64GB of RAM

Specification for node and VM guest are below

Node :

CPU usage 10.48% of 24 CPU(s)	IO delay 0.04%
Load average 2.51,2.00,1.13
RAM usage 16.08% (15.16 GiB of 64.33 GiB)	KSM sharing 0 B
/ HD space 0.22% (2.16 GiB of 976.64 GiB)	SWAP usage N/A
CPU(s) 24 x Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz (2 Sockets)

EMBY Guess (Windows 10) :

CPU 8 cores, RAM 31

Veeam Backup Guess (Windows 2019 server)
CPU 6 Cores, RAM 16

Problem was when running those 2 VMs together. I/O Delay was about 20%-30%. EMBY was fine but VEEAM was real slow. I meant super super slow when doing backup job. Some of the job failed.

The problem solved when I shut down EMBY server. VEEAM Backup just working great

I think it might come from 3 possibility.

First, VM guess or node itself somehow using more resource than its allocated (maybe in some condition which I don't know).

Second, I/O issue. I am not sure about this because EMBY using hdd internally. I meant in the node itself. However, VEEAM backup to another hdd via NFS. Basically, They are using a difference HDD. EMBY using SAS 15K RPM enterprise grade. NFS using HDD consumer grade.

Third, I over commited CPU core. E5-2430 has 6 core 12 thread for each. It shows in the node that has 24 cores. I assign the total of 12 cores for both VMs.
I am not sure how the core count in this case. 14/10 or 14/24

I want to make sure the cause of this before I buy new SDD.
Any idea? Thank you for sharing.

 

[Dunuin]

You are provisioning virtual RAM to the VMs, not physical RAM. The KVM process that virtualizes your VM is needing some ressources too. And in case you use some caching like writeback it also needs the more of the hosts RAM, the more you write, for caching. In case you use ZFS, that will need RAM too. So a VM 16GB provisioned RAM might need 17GB or even more RAM.
You usually don't want to provision more than 80% of your hosts RAM to VMs. PVE needs some GBs too, ZFS might need several GBs and in case your hosts RAM usage exceeds 80% ballooning and KSM will kick in, which will slow down the host and even might force the VMs to kill processes.
And then keep in mind that your RAM can also fragment, so not all of your RAM might be usable.

 

[nwongrat]

Ok got it. Thanks you.

writeback option, Does it good idea to enable it? Some YouTubers do not recommending it . Disable them would make vm run faster but I he did not specific the condition.

 

[Dunuin]

Ok got it. Thanks you.

writeback option, Does it good idea to enable it? Some YouTubers do not recommending it . Disable them would make vm run faster but I he did not specific the condition.

Depends...
Not when not using a UPS and not when using ZFS.