samba - May 2023 - What happens to a Samba share if the shared disk goes offline?

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

On 5/30/23 20:51, Guertin, David via samba wrote:
> 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?
no, Samba doesn't cache created files or directories. Older versions had 
a write cache that could optionally cache recent writes to a file, until 
the file handle got closed by the client, but this cache has been 
removed quite some time ago.

So I guess what happened is that all the stuff that got added by the 
clients was lost due to the filesystem corruption on the server.

-slow

-- 
Ralph Boehme, Samba Team                 https://samba.org/
SerNet Samba Team Lead      https://sernet.de/en/team-samba
SAMBA+ Samba packages                   https://samba.plus/

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