Nas

rsync into an encrypted APFS sparse bundle stored on an SMB share failed on every write with error 45. The files were fine. APFS inside the image needs F_FULLFSYNC on the band files, the NAS's SMB server doesn't support it, and a short Python probe proves it.

A backup job on a macOS SMB share kept dying with EBADF. The NAS stalled under load, macOS reconnected without a word, and because the old SMB 2.1 server granted no durable handles, every open file on the share went bad, including the bash script that was running. Only the kernel log says so.