Migrating a Synology NAS to a UniFi UNAS Pro 8 with Robocopy, SMB Multichannel

The author, who has run a Synology NAS for years, began moving its contents to a new Ubiquiti UniFi UNAS Pro 8. Expecting a routine SMB file copy over a recently upgraded 10 GbE network, they instead spent an evening debugging. They recall a 2007 blog post advocating Robocopy over Explorer for large file transfers, and note that the /Z restartable flag that was helpful then became a major slowdown now.

Initial copies using Explorer produced "The requested operation could not be completed due to a file system limitation" errors on files like \\server\music\Athlete\Tourist\05 Wires.m4p. Switching to Robocopy consistently failed at 92% with Windows error 665 (0x00000299). To isolate the failure, the author copied the file from the Synology to a local Windows desktop, which succeeded, then from the desktop to the UNAS, which failed identically, proving the problem lies in writing to the UNAS.

The author then pivots to Alternate Data Streams (ADS), a Windows NTFS feature they had discussed in 2003 and 2007 in the context of Zone.Identifier, implying this may be the underlying cause. The narrative sets up ADS as a likely lead, though the excerpt stops before a confirmed solution. This highlights how modern NAS devices can trip up long-standing Windows file-copy assumptions.