[Samba] What happens to a Samba share if the shared disk goes offline?

[Guertin, David]

We had a recent data loss event that we're trying to analyze to learn what happened. On one of our Linux VMs, the /var partition suddenly went offline, which is never a good thing. (Later reboots revealed a corrupted filesystem that needed to be repaired, resulting in data loss.) Nothing could be written to /var, including logs in /var/log, but the VM continued to run.  On that VM, we had a Samba export of a directory under /var. Users that had the volume mounted on their Windows workstations could continue to see the directory and write to the share, and everything appeared normal to them, until we rebooted the server and everything went away. Of course the volume was backed up, but there was nothing there because nothing had ever actually been written to disk.

I'm just trying to understand Samba's role in this, and how users could see files, and write new files, when they weren't actually on the underlying disk. Does Samba keep its data in memory even if the disk it's sharing goes down?

Thanks,
David Guertin