ReadyNAS Duo Rsync from Linux

I am rsync'ing from Linux. The backup folder on the NAS has been mounted as an NFS share. Typically in the past I have backed up just my own data from the linux box (corresponding user exists on the NAS) and that seems to have worked ok.

Now I want to back up some third party files that are owned by a mixture of root and informix - I have a corresponding informix user on the NAS. I use sudo rsync -auv . /mnt/NAS/backup/OLD-INFORMIX. That does the backup, but all the files on the NAS than appear to be owned by nobody:nogroup - although at directory level, the ownership appears to be informix:informix as would be expected. I get the same issue if I actually become root locally and then rsync the files as the root user.

I can log in locally as informix and then use rsync as informix, but that then fails to copy the 'root' owned files.


Any idea why the sudo / root copy is not preserving the ownership details on the NAS?


Edited to add: If I back up as Informix and the file is root:informix with rw.r.r, then the file is copied as informix:informix with rw.r.r - if the file is root:informix with just rw at owner, then the file isn't copied (as would be expected).