I have a QNAP NAS that I would like to use to back up my Photo library.
I know that there are some restrictions for the Photo library, for example it says that you should not use Time machine to back it up if it is on an external drive.
Is there any problem copying the Photo library to the QNAP?
I could find out if there’s a way to create a RAID drive that’s APFS on the Qnap but that would involve more research.
Can you back the Photo Library up to Dropbox or Google Drive?
AFAIK Apple doesn’t say anything about a NAS but it does say “Make sure that your external storage device, such as a USB drive or Thunderbolt drive, is formatted for Mac: either APFS format or Mac OS Extended (Journaled) format.”
My Photos library is on a direct attached SSD and I also back up everything automatically to Google Photos.
No. APFS can only be used on drives directly attached to the Mac. The NAS does not support formatting its drives using the APFS filesystem—it has to use the filesystems native to variants of Linux used on NAS boxes, which are usually ext3, ext4, and, most recently (and recommended as being the most advanced), btrfs. Your Mac uses the SMB protocol to access the NAS and does not care (or actually know) what the underlying filesystem on the network share is (it could be anything, including NTFS for Windows shares – that’s the point of using network protocols such as SMB and the older AFP).
That said, Apple advises against storing Photo Library on any device that might suddenly disappear, including network drives, to avoid data loss.
And to avoid possible data loss, don’t store your library on a removable storage device like an SD card or USB flash drive, or on a device shared over your network or the internet, including over a cloud-based storage service.