Hardware-Requirements: 16GB RAM not enough?

[whiterabbit]

Hi. We use a Proxmox-Server with
pve-manager/2.3/7946f1f1

The Server has 16 GB RAM and a RAID-10. Besides there's a 1TB-SATA-backup-HDD.
At the moment we use 4 VMs (all KVM).
They use 1GB + 6GB + 1GB + 2GB = 10GB RAM. So the rest should be enough for the proxmox-host.
I tried to make a filebased backup from the "6GB-VM" (Ubuntu) to a NFS-Share. This was horrible slow and took over
24h to run. When I stopped one VM with 1GB RAM it ran as fast as it should.
My question is: How much RAM does the Server need to run performant?
Obviously 6GB is not enough?

 

[beta17]

i don't think that's memory related!
have you monitored the vm/server/nfs during the backup?

 

[whiterabbit]

i don't think that's memory related!
have you monitored the vm/server/nfs during the backup?

I looked at "htop" on the proxmox-server and at "htop" on the VM -- both had nearly nothing to do.
CPU was at about 20% ....
But the rsync-Process was VERY slow -- I wanted a filebased backup of /home (100GB) and it took 24h to transfer 12GB (!!!). Then I switched off one of the other VMs and the rest went fast.... so: Where to look?

 

[m.ardito]

My question is: How much RAM does the Server need to run performant?
Obviously 6GB is not enough?

Hi, one of my nodes is currenty running no VMs, it has 20GB total ram, using around 350 MB for itself...

Another identical node in the cluster now has 15 kvm and 1 openvz, always with 20GB total ram (using around 16.5 GB for itself + kvm + openvz)

Marco

 

[Raymond Burns]

Sounds like it's I/O related. I would benchmark your disk reads and writes while under operation.

 

[wahmed]

My question is: How much RAM does the Server need to run performant?
Obviously 6GB is not enough?

It is definitely not the RAM. Just to give you an idea, i have a 32GB Proxmox Node which is running 57 VMs with avg. of 1.5 GB RAM. Proxmox has a feature call KSM Sharing which auto allocates unused RAM to the VM which needs RAM allowing you to increase VM density per node.

I tried to make a filebased backup from the "6GB-VM" (Ubuntu) to a NFS-Share. This was horrible slow and took over
24h to run.

Were you doing the backup from inside the VM? This does not sound like you were doing the backup using Proxmox VZDUMP backup option. What is the OS of the NFS Server machine you are trying to backup to?

 

[udo]

... Proxmox has a feature call KSM Sharing which auto allocates unused RAM to the VM which needs RAM allowing you to increase VM density per node.
...

Hi,
AFAIK KSM used same RAM-content only one times - if you have VMs with the same OS KSM will free memory for you (but need CPU-Power).

Udo

 

[wahmed]

AFAIK KSM used same RAM-content only one times - if you have VMs with the same OS KSM will free memory for you (but need CPU-Power).

You are very right Udo. I think i worded it wrong from what i wanted to express. KSM works with same type OS. According to Wiki, Proxmox KSM scans all memory blocks then combines all duplicates thus freeing real memory. KSM is great when a node has higher number of same OS. The reason one of my node is running that many VM at the same time is because they 90% of the VMs Windows XP.

 

[mir]

The summary view of the host will show the current size of shared KSM.

 

[whiterabbit]

Sounds like it's I/O related. I would benchmark your disk reads and writes while under operation.

How to figure out that? Maybe with "atop"?

Were you doing the backup from inside the VM? This does not sound like you were doing the backup using Proxmox VZDUMP backup option. What is the OS of the NFS Server machine you are trying to backup to?

I installed NFS on the Proxmox-Server itself because I thought that this might be the fastest protocol to move some data from a VM to the proxmox-host itself. I also tried "qm set" to share a HDD with a VM but this was not very fast as well. But as I told before: It works -- but it's slow.