Network Appliance Virtual Hosting Fun Stuff

[deanwebb]

Just found out today that very very small Nutanix environments do NOT like network appliances with 8 cores, 16GB RAM, and 2 NICs running on them. One group installed one of our NAC boxes on a Nutanix and another group noticed 6 weeks later and threw a red flag on us.

He was particularly upset about the cores, since the box itself only has 6...

[Dieselboy]

Firstly, Nutanix?
Secondly, how were they able to provision 8 cores when the hardware only has 6?

[wintermute000]

You can give a vm as many virtual cores you want

[deanwebb]

Dieselboy: Nutanix is cheaper than VBlock. Therefore, it is more scalable from a financial perspective.

This is me using up all the resources on the littlest, cheapest Nutanix installed at that site and then the VM team's response:


I'm the guy on the right, this time. 

[wintermute000]

Hyperconverged and / or distributed storage (ceph) is the future. Vblock and flexpod is so 2014. [emoji14]
Mythos
Nutanix, EVO with vsan etc the tide is coming

[Otanx]

We had Nutanix do an on site class last Friday. We have had a demo appliance for awhile, but no real time to learn it. It was pretty nice. I actually like their hypervisor. I didn't know you could get boxes that small.

-Otanx

[Dieselboy]

You can give a vm as many virtual cores you want

But what is the point though if the physical hardware has X number. Surely the formula for virtual cores is 0>&<X where X is the hardware core's. Is there any benefit to giving a VM more virtual cores than the physical hardware has? I can only think that it would impact performance?

[wintermute000]

Yes it kills performance. But the question was can you, not would you want to

[Dieselboy]

 

[deanwebb]

My thoughts exactly... but if one has three servers that ask for 4 processors each, but they only really run on 2 most of the time, then they can fit nicely on a 6-processor box. If, however, it's a server that EXPECTS those resources 100% of the time because it doesn't know it's not really hardware, then it can sometimes delay or fail because the resources are not released to it.

My NAC box demands those resources... the Windows servers on that Nutanix are not getting the resources that they want.

[Dieselboy]

Are you guys saying that people do this in production?

[deanwebb]

Yes. All the time. It's basically "thin provisioning", the computational equivalent of fractional-reserve banking.

[Otanx]

Are you guys saying that people do this in production?

By "this" do you mean assign more virtual cores to a single VM than the hardware has? No, not usually done unless someone goofs. However, if you mean assign more virtual cores than the hardware has across multiple VMs with no single VM having more than the hardware. Yes, all the time. As Dean said most systems don't use all their cores all the time so I can get away with over subscribing my physical cores knowing that not all the systems will try to use all the cores at the same time. This is also done with RAM and storage. One of our customers that tracks their over subscription has (IIRC) 4:1 over subscription on cores, and RAM, and something massive like 300:1 for disk space. Over subscription is one of the big benefits of virtualization.

-Otanx

[Dieselboy]

I was referring to giving a single VM more CPU than exists in hardware.

On our RHEV environment we generally run up to 90 VM's on 2 physical hosts. Each host having 128GB RAM and 24CPU threads (two Xeon CPUs with 6 cores each, hyperthreaded).  RAM is overallocated by 150% but we have been discussing reducing this to 100%. Storage was in the 1000% range when I first joined here but have this down to 92% one one volume and 150% on the other.

[wintermute000]

I was referring to giving a single VM more CPU than exists in hardware.

That's still a no-no but the software won't stop you from doing it, and it will 'work', just badly