I've got a new Unraid setup. Often when I try to copy files from my Unraid share to my Mac, I get errors. In the Unraid log I see e.g.

Aug 20 15:14:14 Blockhead smbd[3832672]: [2025/08/20 15:14:14.982291, 0] ../../source3/smbd/smb2_read.c:264(smb2_sendfile_send_data)

Aug 20 15:14:14 Blockhead smbd[3832672]: smb2_sendfile_send_data: sendfile failed for file xxx.mkv (Broken pipe) for client PID=3832672,CLIENT=2888d4b6-612a-174c-a793-a2d33caed956,channel=0,remote=ipv6:2404:e80:67ee:0:8909:83b2:83c8:3346:63877,local=ipv6:2404:e80:67ee:0:c662:37ff:fe02:4526:445. Terminating

Sometimes a file transfer works, but it's pretty easy to repro this just by trying a couple of file transfers.

Any ideas?

In case this helps anyone in the future I solved this problem by disabling samba sendfile.

UNRAID - Settings - SMB. In SMB Extras add a line "use sendfile = No".

The SAMBA default setting for sendfile is No but UNRAID sets it to Yes. According to the internet sendfile and zfs have issues. In my case I was transferring from a zfs pool and disabling sendfile fixed it.

Perhaps it would behove UNRAID to leave this setting at the default of No as it seems it is disabled by default for a reason.