Looking for detail regarding the VDI optimization of HyperFlex

[SIMMN]

When setting up the HX cluster, there is the option for "VDI Optimization"...What kinda magic does this option do really if I selected it for the cluster? Can this option be modified post cluster installation?

From the HX whitepaper linked below, 

"Only select the options VDI or VSI when installing HyperFlex on a hybrid system. If you are running mixed VDI and VSI workloads, do not select this option. Only select this optimization when running VDI desktops, and only on hybrid HX models. This option is only shown during the “I know what I am doing” installation workflow."

https://www.cisco.com/c/en/us/products/collateral/hyperconverged-infrastructure/hyperflex-hx-series/white-paper-c11-744135.html

Assuming the cluster would only run Citrix VDI but what is a "hybrid HX model"? The SSD and HDD hybrid?

[RedNectar · Accepted solution]

Hi @SIMMN ,

What kinda magic does this option do really if I selected it for the cluster?

Secret magic. Which may vary from version to version I believe. Hopefully someone can give a better answer, but I suspect even if they can, they'd be reluctant to say too much.

Can this option be modified post cluster installation?

Not without TAC support I believe. Probably easier to backup, reinstall, restore.

what is a "hybrid HX model"? The SSD and HDD hybrid?

Correct. HyperFlex comes in 3 core flavours. 

1. All NVMe flash: Optane Cache and NVMe capacity disks
2. All Flash: NVMe cache and SSD capacity disks
3. Hybrid: SSD cache and HDD capacity disks

I hope this helps.

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[SIMMN]

Okey, wonder how could I know if a running cluster has the VDI optimization option enabled?

[Steven Tardy · Accepted solution]

From the CLI you can run:

root@SCVM01:~# grep workload /etc/springpath/storfs.cfg
workloadType=Vsi

Like stated above VSI vs VDI only changes if the cluster uses non-SSDs/spinning/HDDs for persistent disks which Hyperflex calls "Hybrid".

There are some caching and block size changes under the hood to optimize the read/write pattern of VDI environments.

The VSI vs VDI can be changed after the fact by TAC but not something which is done very often.

[SIMMN]

Cool, if the command output shows VDI instead of VSI, it means the cluster was built with the VDI optimization checked, right?

[luizlalmeida]

Hi,

This is an old thread but I believe it´s useful to clarify the issue and doubt.

When installing HyperFlex you can choose a VDI optimization option in the installer. This option will omit the most recently written data to be cached on write. This write-through approach allows more of the most commonly (frequently) used data to be held in cache directly. VDI applications usually do not benefit from having access to the most recently used information provided in the read cache, so we can discard it and leave room for the most frequent data.

All-Flash and All-NVMe deployments do not use any read caching and therefore do not have any VDI optimization option available.

Hope this helps.

Luiz