Locking with CTDB

[Henning Henkel]

Volker Lendecke schrieb
> For general samba-style locking this would be far, far too
> slow though. Thus the need for ctdb. Ctdb stores its
> databases in normal tdb files that require fcntl locking,
> but this time these files are not stored in the cluster file
> system. They are stored on local ext3 or so where fcntl
> locking is fast. It is the main task of ctdb to work around
> the slowness of the cluster file systems for small requests
> and locking, making use of the fast local file systems.
>   
Thanks for your answer. Trying to dig in a bit deeper, I set up the 
following test scenario:

I have a ctdb installation running samba on two nodes. The ctdb lock 
file and a test share A reside on a shared filesystem that supports 
consistent locking across nodes. When I cifsmount this share from 
several clients through different server nodes in the ctdb cluster and 
try to acquire Posix locks on a shared file, locking works as expected. 
When I set up a second share on a filesystem with (OCFS2-like) locking 
that is locally consistent only, and cifsmount this share to several 
clients via different samba servers in the ctdb cluster, I can acquire 
multiple locks for the same shared file simultaneously.

That's the thing that makes me a little curious, as I would expect, that 
samba/ctdb would handle the locking also in the second case. Still, the 
underlying filesystems locking semantics seem to make the difference, 
and a lock on the shared filesystem is acquired by samba in any case. Is 
this the way ctdb is supposed to work, or is there still a bug lurking 
in my test setup?

Henning

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