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Re: [Linux-cluster] Asking information about NFS /CS4 Cookbook



On Thu, 2007-05-24 at 06:31 -0400, Fajar A. Nugraha wrote:
> Hi Wendy,
> 
> Wendy Cheng wrote:
> >>> - can the client handle the change gracefully so that
> >>> there will be no "stale nfs handle"?
> >>
> >
> > This is a tough problem to solve. Hopefully the bugzilla entry
> > explains well.
> >
> The bugzilla does say a lot. Thank you.
> >>>
> >>> On the server side :
> >>> - When the exported filesystem is non-cluster (e.g. ext3), how
> does the
> >>> server handle locking issues? If an nfs-client is locking a file,
> can
> >>> the server (in Managed NFS service) forcefully unmount the file
> system,
> >>> considering that the nfs daemon is kernel-space, so that it can't
> be
> >>> killed?
> >>
> >
> > We have a tentative patch set for this. It is usable but still under
> > revised.
> >
> Please help me go through this summary from the bugzilla
> 
> Before we complete the work, for NFS v2/V3, RHEL 4.4 has the following
> restrictions:
> 
> ==> Is this still valid for RHEL 4.5 and RHEL5?
> 
> B-1: Unless NFS client applications can tolerate ESTALE and/or EPERM
> errors,
>      IO activities on the failover ip interface must be temporarily
> quiesced
>      until active-active failover transition completes. This is to
> avoid
>      non-idempotent NFS operation failure on the new server. (check
> out
>      "Why NFS Sucks" by Olaf Kirch, placed as "kirch-reprint.pdf" in
> 2006
>      OLS proceeding).
> 
> ==> What does this mean, exactly? For example, does this mean that I
> should not use RHCS-nfs-mounted storage for
> busy-accessed-all-the-time-web-servers because I'd likely get
> ESTALE/EPERM during failover?
> 
> B-2: With various possible base kernel bugs outside RHCS' control,
> there
>      are possibilities that local filesystem (such as ext3) umount
> could
>      fail. To ensure data integrity, RHCS will abort the failover.
> Admin
>      could specify the self-fence (reboot taken-over server) option
>      to force failover (via cluster.conf file).
> 
> ==> In short, it'd be better using GFS, right?
> 
> B-3: If nfs client invokes NLM locking call, the subject nfs servers
> (both
>      taken-over and take-over) will enter a global 90-second (tunable)
>      locking grace period for every nfs service on the servers.
> 
> ==> What does "locking grace" mean? Does it mean read-write access
> allowed but no locks, or no acess at all?
> 
> B-4: If NFS-TCP is involved, failover should not be issued on the same
> pair
>      of machines multiple times within 30-minute period; for example,
>      failing over from node A to B, then immediately failing from B
> back to
>      A would hang the connection. This is to avoid TCP TIME_WAIT
> issue.
> 
> ==> So what does this mean currently in TCP vs UDP world? Does it mean
> nfs v3 UDP is the preferred method?
> 
> >>> - Can the client gracefully handle new, failover,  nfs clients,
> since
> >>> some nfs information is stored on /var/lib/nfs, which is on a
> local
> >>> file
> >>> system?
> >>>
> >>> 
> >>
> >
> > This would need to be moved into the shared storage area (and done
> by
> > RHCS).
> >
> Okay, this one makes sense.
> That means there's an additional step involved here, not mentioned
> (yet)
> in nfs cookbook, right?
> 
> Regards,
> 
> Fajar
> 
> 
> 
> --
> Linux-cluster mailing list
> Linux-cluster redhat com
> https://www.redhat.com/mailman/listinfo/linux-cluster
> 
> 
> 
Just want to say great thread and I am very interested in setting up a
highly available nfs file server.  The caveats mentioned so far would
have gone completely overlooked.  Thanks


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