@Huang, Winston-HR Welcome to Microsoft Q&A Forum, Thank you for posting your Query here!
It's not clear what you mean by "incur the same cost." If you're asking whether the two volumes will cost the same amount to use, then the answer is yes, assuming they are both using the same Azure storage account and access tier.
Regarding your question about cluster size, it does not directly incur a cost. However, the cluster size can affect the amount of space that is used by Azure File Sync metadata and heatstore, as well as the amount of free space that needs to be reserved on the local disk. In general, larger cluster sizes will require more space for metadata and heatstore, and will also require more free space on the local disk.
It's important to note that the cluster size can affect how efficiently space is utilized on the disk. In the context of NTFS, the cluster size determines the smallest amount of disk space that a file can occupy. Smaller cluster sizes can be more efficient for storing small files but may lead to more significant overhead for larger files, as they occupy whole clusters even if they don't fully utilize the space.
Based on your scenario: I would recommned to contact Azure Billing and Subscription team would be the best to provide more insight and guidance on this scenario: https://azure.microsoft.com/en-us/support/options/ it's free, and it's the best choice for you.
Please let us know if you have any further queries. I’m happy to assist you further.
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