Dear Miguel
When you mentioned "client Red Hat LPAR", I assume that your created NWSSTG objects (virtual disk device) in IBM i Host LPAR for the client Red Hat LPAR. If this is the case and if the LTO8 device can already be used by the host IBM i LPAR, then you can use it to do the backup of the entire storage space of each Red Hat client LPAR by saving its corresponding IFS file. Look at chapter 8 Backup and Recovery in the attached file " IBM i Host and Client LPARs Easy Install Guide".
To avoid disk response time problem at peak workload period for the client LPAR, make sure you create more than 2 NWSSTG objects for the client LPAR.
But if you want to do the backup from within client LPAR itself using tape device from IBM i host LPAR, you need to configure virtual tape device in IBM i host LPAR and export it to the client LPAR. Read more on how to do this from these info sources:
Requirements for Virtual Tape in i Client Partitions at https://www.ibm.com/support/pages/requirements-virtual-tape-i-client-partitions.
Client virtual devices (optical and tape) at https://www.ibm.com/docs/en/i/7.4.0?topic=storage-client-virtual-devices-optical-tape.
Sharing Tape Libraries Across Partitions Without VIOS at https://www.itjungle.com/2020/05/04/sharing-tape-libraries-across-partitions-without-vios/