you're right regarding the backup itself.
The data is written die NAS attached drives during the backup.
PrimaryCopy only has NDMP attached drives configured as data paths.
But when reading data, my expierience is, that ANY drive capable of mounting the required media connected/configured w/ the MediaAgent used as Source MediaAgent/for reading, is considered valid.
Data paths listed in the SPC are not prioritized over other available drive paths configured to the same library on that MediaAgent.
If you move the tape media to a different library it is not required to adjust data paths in the SP/SPC to read the data from that tape media. Only if writing is intended, valid data paths have to be defined in the SPC.
For restores you are able to restrict read operation to a specific drive pool, for auxcopies can only be restricted to a MediaAgent.
The destination drive pool has data paths to a different library only. Therefore this does not interfere.
These drives are not NAS attached anyways.
The MediaAgent used for AuxCopy has the controlling function for the NAS attached drives as well as locally attached drives within the same libary. (I now disabled the local attached drivepool to avoid mounting of media to those drives)
Restore of NDMP data, originally written to NAS attached drives, is absolutely no problem if your MediaAgent only has direct attached drives connected.
Media is mounted to an available drive (e.g. Windows : \\.\Tape0) and restores are processed.
The AuxCopy on the other hand requires NAS attached drives to read the data. (and I don't understand why)
The Resource Reservation Cache option is NOT checked in the StoragePolicy settings.