Do you mean "why we are using data disks attached to a VM if data could be stored directly in a Storage Account"?
If so:
A Storage Account is a "serverless storage" to store data. You are able to access the data without running a VM from internet and/or VMs in Azure.
A Storage account (fileshare or blob storage for example) can be used by a VM like a "network share"
A data disk is always attached to a VM. You can't access the data on the data disk directly from internet.
For the VM OS the data disk is attached to the VM and can be used by the OS and services like a "local disk" in your computer.
Does this help?
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten
That was crisp and well explained! Thanks
Thank you so much.