Subject: RE: Does NFSv4 support file change notification ?

From: "Yoder, Alan" <[email-masked]>
Date: Wed, 26 Jan 2000 09:11:08 -0800

> Roland Mainz wrote:
> > Does NFSv4 support change "notifications" a file/directory, e.g. if
> > someone modifies the file or directory the filesystem sends a
> > signal/message to the requesting client ?
> 
> No.  Change notification doesn't scale.  Imagine the scenario of
> several hundred clients registering notification on a single file
> followed by one or more clients changing that file frequently.

   NT does this, though, as Guy mentioned.  How compatible with NT 
does the group want to be?  Doing GUI exploration--from a Win32 
interface--of an NFSv4 volume without change notification won't 
work the same as exploration of an NTFS volume.  And any other
NT apps that depend on change notification to decide when to take
some action won't work correctly when the filesystem is NFSv4.
   Furthermore, I've seen very little evidence that the pathological 
cases you mention actually happen very often in practice. 

   All that said....

> As a practical matter, the NFSv4 specification is currently closed
> to new functionality and is going through final reviews on its way
> to the IESG (new version NFSv4 draft should be out in a day or two).
> NFSv4 does have a minor versioning mechanism.  Therefore, if, at a
> later time, notification becomes a hard requirement with reasonably
> scalable solutions, the functionality can be added to NFSv4.

   I agree that this is the wrong time to be discussing it.

Alan

===============================================================
Alan G. Yoder                                    [email-masked]
Network Appliance, Inc.                           
Santa Clara, CA                                    408-822-6919
===============================================================

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From: Guy Harris <[email-masked]>
Date: Wed, 26 Jan 2000 12:19:52 -0800 (PST)

> work the same as exploration of an NTFS volume.

Only if the NT or W9x NFS client in question doesn't support change
notification; it could do change notification by periodically doing "get
attributes" requests on all the files it needs to look at.  Given that
V2 and V3 have no change notification mechanism, I wouldn't be surprised
to hear that at least some NT or W9x NFS clients do exactly that.

Note that the Win32 change-notification request can say not only "let me
know if anything in this directory changes" (change notifications are
posted on directories, not files, as I remember), it can also say "let
me know if anything in this directory *or any of its subdirectories*
changes.