Strange NFS-related messages (related to lockd/statd)

[Rick Macklem]

On Mon, 29 Mar 2010, Jeremy Chadwick wrote:

>
> I can't find a definition of what the acronyms NLM and NSM stand for,
> nor does Googling the error messages return relevant results (except one
> FreeBSD committer reporting similar, but nobody replied).  I don't know
> the implications of these messages.
>

NLM - Network Lock Manager
NSM - Network Status Monitor (I think?)

These two protocols (separate from NFS) were what Sun implemented in
the 1980s to provide locking on NFS mount points. Imho, these protocols
were poorly designed:
- The NLM allows blocking locks at the server, which can cause assorted
   nasty issues when the client crashes or gets network partitioned.
- It also depended on the NSM to decide when machines were up/down and
   the NSM protocol basically did this in a rather poor way.

A big part of NFSv4 was the integration of locking, in order to avoid
use of the above. (As you might have guessed, lockd and statd implement
the above two protocols.

rick