[heketi-devel] How can Heketi decide about SSD and HDD bricks

John Mulligan phlogistonjohn at asynchrono.us
Thu Aug 20 13:32:45 UTC 2020

On Wednesday, August 19, 2020 11:37:18 AM EDT Volker Dormeyer wrote:
> Hello all,
> I am new to this list.
> I plan too build a cluster, which should be accessed from multiple
> Kubernetes clusters, with SSD and HDD storage. The SSD should pooled
> together and HDD should be pooled separately. How can I decide which one of
> the both pools should be used?

By default the system doesn't know that the devices are of different types. To 
separate them you'll probably want to make use of the tag-matching feature 
(see: https://github.com/heketi/heketi/blob/master/docs/design/tag-matching.md 
for more details).

> Through two different storage classes?

Yes, once you've separated your devices you would need to create at least two 
storage classes each with the proper volume option to select the tags using 
user.heketi.device-tag-match volume options.

> Through a parameter in the topology?

You can set tags via the topology but it doesn't help with the selection of 
devices. I don't really recommend the topology load for doing anything other 
than initial bootstrapping though. It doesn't handle updates well.
I simply recommend using the various heketi-cli commands after the initial 
topology is loaded but before you start creating PVCs.

If you have any additional questions, feel free to ask. These are relatively 
new features.

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