The server has a single 70tb raid 6 array on a Perc H710. This is approaching capacity. I’m going to add another controller and a DAS with 60tb of raid 6 storage. There is no way to simply ‘merge’ these into a single drive letter or path.
I’m not sure why backup location can’t be specified per client or have multiple locations.
What kind of OS?
On linux, if you use LVM, you can add new volume to VG and extend LV.
R.
Windows Server 2019
You can use storage pool on WS to spread a volume over multiple disks. I don’t have a ready example to share, so you need to google it, but it can be done.
R.
I’ll look into it. Thanks!
Looks like I would have to delete the existing storage. Thats not going to work. 
What about creating new volume as a dynamic in the new storage pool, moving over current backup directory there and than adding old storage to the new pool? Would that work?
Not sure I’m going to have enough space. Existing volume is 70tb and close to being full. New volume is~60tb
But thats an excellent idea. 
Make it RAID 5 instead of 6 - you will get more space
I want the double redundancy. I’ve seen a drive fail during a r5 rebuild.
Am sure you can set a location on a per client basis, go Settings > Client (select client) > tick “Separate settings for this client” > and somewhere in there is a bit you can specify a different storage location…it might not show in a mobile browser, so I couldn’t find it when typing this up…
You can not.
Also, know that you can migrate from one location to another, had to do that myself shortly after starting…