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Mixing Hybrid with All Flash Nodes

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Trailblazer

Mixing Hybrid with All Flash Nodes

With 5.1, is it possibel to mix 2 x Hybrid Nodes with 2 x All Flash Nodes or do we still need to have 3 x Hybrid Nodes and 2 x All Flash as a minimum?

13 REPLIES
Nutanix Employee

Re: Mixing Hybrid with All Flash Nodes

When adding any different node type it's preferred to add them in pairs, this is a must if adding nodes with larger capacity than existing ones.

 

In your example 2x hybrid and 2x AF nodes would be fine. Just use matching hybrid nodes and matching AF nodes. 

Trailblazer

Re: Mixing Hybrid with All Flash Nodes

briansuhr wrote:

When adding any different node type it's preferred to add them in pairs, this is a must if adding nodes with larger capacity than existing ones.

 

In your example 2x hybrid and 2x AF nodes would be fine. Just use matching hybrid nodes and matching AF nodes. 


 

Thanks for the quick response. In this scenario is it still possible to enable Erasure Coding if having 2 x Hybrid and 2 x All Flash?

Nutanix Employee

Re: Mixing Hybrid with All Flash Nodes

Hello,

 

Yes erasure coding will work normal with this config, min number of 4 nodes is met.

Trailblazer

Re: Mixing Hybrid with All Flash Nodes

Would there be an issue if only 1 All flash node was added to a 3 node hybrid cluster? I can understand that performance may drop when doing live migration or reading from node having data on the cold tier but wouldn't that be the same regardless if having 2 all flash nodes, that the RF Data could sit anywhere in the cluster and not just on the other all flash node?

 

Nutanix Employee

Re: Mixing Hybrid with All Flash Nodes

While this should be technically possible, it would not be a recommended configuration. When adding a different node type to a cluster it's recommended to add a pair the first time. By having a pair you are ensured there is rebuild capacity in the cluster for each node type.

 

Your example of 2 hybrid and 2 AF nodes to start a cluster. After that you can add either node types 1 at a time.

 

Trailblazer

Re: Mixing Hybrid with All Flash Nodes

Is that only capacity constraint? Considering that an all flash node would most likely be smaller storage than a hybrid, I was wondeirng where the bottleneck would be.

 

i am thinking of adding an all flash node with this kind of configuration:

Current Cluster 3 nodes:

4 x 400GB SSD Per Node

6 x 2TB Sata Per Node

 

Additional Node:

10 x 400GB SSD

Guardian

Re: Mixing Hybrid with All Flash Nodes

It's definitely a concern.  In you're current cluster you should have around 1.84TiB of SSD of extent store (see designbrewz image) and the new node is bringing in 1.13TiB of SSD for workload that you are expecting SSD performance for everything that runs on that node.  If the node fails, unless the other workload has used more than .71TiB, you are going to be overflowing the SSD. Buy starting in pairs and using affinity rules you'll be able to ensure that the VM's that expect SSD performance are going to get it if you experience a node failure. 

 

Screen Shot 2017-08-02 at 10.02.07 AM.png

 

 

Nutanix Employee

Re: Mixing Hybrid with All Flash Nodes

The best practice of adding in pairs for different nodes types is both for capacity rebuilds and predictable performance. Having a node of matching capacity will ensure there is space to rebuild should a failure occur. This is of biggest concern when adding nodes with increased capacity to a cluster, not of concern in your case.

 

The second thought is on predictable performance. Should a failure occur much like the rebuild there is resources to provide same matching performance experience. If you added a single AF node and it was the one that failed you would be reverting back to your current performance experience. Which is likely not an issue for your environment, just guidance to protect the general situations. 

 

I would also discuss with your local account team as they should know more about your environment and workloads.

Trailblazer

Re: Mixing Hybrid with All Flash Nodes

Yes in our case capacity is not an issue. As for performance, even if there were a pair of all flash, there is no guarantee that the RF data for the AF node would sit in the other AF node right? Does VM host affinity controls where RF data goes?

I don't mind losing performance if the AF node fails as even the Hybrid Nodes are quite decent specs for our workloads. An all flash would at least guarantee performance even for the cold tier for the most intensive VM sitting on that particular host if I got it right.