Tranfer data to specific drive

I have just purchased a My Cloud EX2 Ultra 8TB. As I do not wish to duplicate the data on the device, I have set the device up in JBOD mode. It appears that the two drives or volumes are seamless.
Is it possible to transfer data (a specific folder structure) to one specific drive of the two drive unit, and if so how?
The reason I wish to do this is I have two sets of data to backup: one set accessed frequently (daily) and one set accessed infrequently (monthly). Each set assigned to a different drive. I expect the drive used frequently will fail before the drive used infrequently.
I should add Spanning is Off.

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