CVM Resources Allocation

  • 23 January 2017
  • 8 replies

Userlevel 1
Badge +2
Hey Everyone. So, I am relatively new to the whole Nutanix game.

Im curious what everyone is suggestion is for CVM allocation. We had nutanix do our original provisioning, but the provisions the installer set it up with seem a bit excessive. 10 Cores and 32gb ram per CVM,

Any thoughts?

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8 replies

Userlevel 2
Badge +19
Right now deault is 24gb and the same number of vCPUs as one processor. It depends on how much you have the CVM doing. If RF3, dedup/compression and replication with frequent snapshots, you may need more. If it's just basic storage and nothing else, then you might need less. It might be worth a quick call to support just to have them give it a look over and give you a recommendation.

Installation environment today usually isn't the same environment six months later.
Userlevel 6
Badge +29
That last setence is the most telling. Day 1 utilization isn't the best gauge of how large a cluster should be sized.

By default, the installer will set the number of vCPU's on a single CVM equal to the number of cores on one single socket, with some top end limitations.

Guessing you've got 10 core processors in those boxes, hence the 10 vCPU setting.

Note that those are not reserved CPUs. In the ESXi world, we reserve 10GhZ of top end CPU, which only comes into account when there is 100% CPU contention on the box. Thats roughly equal to around 4 cores. This is a good thing, as you wouldn't want the CVM's to be starved for CPU when you're really hammering on the box.

Same deal with CVM memory, with the exception that those are hard reservations, so we statically reserve whatever memory is allocated. Same principle, you dont want the CVM's starved if you're really running hard.

As for configuration setting of memory, minimum used to be 16GB, now the absolute floor is about 24GB as of AOS 5.0.

32GB, at minimum, unlocks capacity tier deduplication if you choose to enable it.

Keep in mind, we dont use that memory for nothing, thats caching, and other fancy stuff designed to make the system run better, or deliver killer features back to you.
Badge +3

Is there a Offical word out there for CVM sizing. I am working on a Low level design document for implementing a big Data Centre ( 100 + nodes ) based on nutanix Nodes over DELL XC630 boxes. We plan to use AOV 5.0.3 with ESXi 6.5. Same time we plan to use ultimate licence with features like Dedup / complression /erasure coding etc. Another aspect is the recommended cluster size. While Vsphere 6.5 supportes upto 64 Hosts in a cluster, I am unable to find any equivalent documentation from nutanix.
Userlevel 1
Badge +9
With just the core features you have listed, 24GB per CVM is probably fine but if you plan to use other services like AFS or self-service, then 32GB would be a good size to start at for a bit of future proofing.
There really is no limit to the size of a Nutanix cluster. If you were using the Acropolis hypervisor, you could have 100's or 1000's of nodes in a single cluster. With vSphere being the hypervisor, you're limited to 64 nodes per cluster. In my environment we limit cluster size to 32 nodes just because self-imposed restrictions on rack capacity and how we implement failure domains.
Badge +3

I understand . What i am looking for is a official document from Nutanix guiding the CVM sizing and considerations for same. I did found one "Configuration Best Practices for Nutanix Storage with VMware vSphere" but document is 2014 vintage and perhaps outdated as well
Userlevel 6
Badge +29
sushilkm - thanks for reaching out, hope the holidays treated you well.

The guidance you're looking for is here:

Second link is under the AHV docs, but the guidance is the same for ESXi.

TLDR - 32GB is a pretty solid recommendation. You can trust mikegelhar - he runs one of the largest Nutanix deployments in the world and has seen pretty much everything there is to see 🙂
Badge +2
Folks, could you confirm if we should be setting CPU\RAM Shares, Reservations and\or Limits on the CVM (when using ESXi) ?
Userlevel 3
Badge +8
The AHV documentation says that you can go higher on vCPU and RAM for the CVMs based on your install base [cores in physical CPU] and workload [see attachment]