Thanks for your question. For optimized performance we do recommend using ephemeral OS disk for AKS. Details about this can be found here. Ephemeral OS disks are stored only on the host machine, just like a temporary disk. With this configuration, you get lower read/write latency, together with faster node scaling and cluster upgrades.
When selecting the VM size for your node pool you can filter if Ephemeral OS disk is supported.
Unfortunately, I am not able to share the specifics of why the Dadsv6 does not support ephemeral OS disk. I believe this could be related to v6 utilizing NVME disks. I would recommend sticking to Dadsv5 or Ddsv5, AKS will update the recommended VM types when new ones become available.
Hope this helps! Let me know if you still have questions and I will do my best to assist.
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