NFS & Clustering

NFS & Clustering

[Marco.Schwarz]

Hi all,

we are looking into the possibility of building a clustered NFS-root server
for our diskless clients. Does anybody know if this is possible with NFS and
which cluster software is best for this task (OpenMOSIX ?).

Thanks in advance,
Marco


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Re: NFS & Clustering

[Bryan O'Sullivan]

On Wed, 2002-09-04 at 01:35, Marco.Schwarz@Freudenberg.de wrote:

> we are looking into the possibility of building a clustered NFS-root server
> for our diskless clients. Does anybody know if this is possible with NFS and
> which cluster software is best for this task (OpenMOSIX ?).

It isn't possible without a modified mountd that replicates mount
information.  I haven't seen any free NFS servers that do this, but I
haven't looked very hard.

	<b


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Re: NFS & Clustering

[Ragnar Kjørstad]

On Wed, Sep 04, 2002 at 09:03:46AM -0700, Bryan O'Sullivan wrote:
> On Wed, 2002-09-04 at 01:35, Marco.Schwarz@Freudenberg.de wrote:
> > we are looking into the possibility of building a clustered NFS-root =
server
> > for our diskless clients. Does anybody know if this is possible with =
NFS and
> > which cluster software is best for this task (OpenMOSIX ?).
>=20
> It isn't possible without a modified mountd that replicates mount
> information.  I haven't seen any free NFS servers that do this, but I
> haven't looked very hard.

Sure it is. mountd writes the information to disk - you just need to
share that info between the servers.


--=20
Ragnar Kj=F8rstad


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Re: NFS & Clustering

[Bryan O'Sullivan]

On Wed, 2002-09-04 at 09:20, Ragnar Kj=F8rstad wrote:

> Sure it is. mountd writes the information to disk - you just need to
> share that info between the servers.

That leaves you with an obvious race condition.

	<b


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Re: NFS & Clustering

[Ragnar Kjørstad]

On Wed, Sep 04, 2002 at 09:22:40AM -0700, Bryan O'Sullivan wrote:
> On Wed, 2002-09-04 at 09:20, Ragnar Kj=F8rstad wrote:
>=20
> > Sure it is. mountd writes the information to disk - you just need to
> > share that info between the servers.
>=20
> That leaves you with an obvious race condition.

For active/passive systems there are no race-conditions and it works
fine. For active/active systems there would be a race, but it still
wouldn't work because the data is (AFAIK) not reread from disk.


--=20
Ragnar Kj=F8rstad


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Re: NFS & Clustering

[Emanuel Quass]

Hi,

but doesn't it work if you share /var/lib/nfs/* (containing etab, rmtab, =
sm, =20
sm.bak, state, xtab)?

MfG
=09Emanuel

Am Mittwoch, 4. September 2002 18:03 schrieb Bryan O'Sullivan:
> On Wed, 2002-09-04 at 01:35, Marco.Schwarz@Freudenberg.de wrote:
> > we are looking into the possibility of building a clustered NFS-root
> > server for our diskless clients. Does anybody know if this is possibl=
e
> > with NFS and which cluster software is best for this task (OpenMOSIX =
?).
>
> It isn't possible without a modified mountd that replicates mount
> information.  I haven't seen any free NFS servers that do this, but I
> haven't looked very hard.
>
> =09<b


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Re: NFS & Clustering

[Bryan O'Sullivan]

On Wed, 2002-09-04 at 09:24, Emanuel Quass wrote:

> but doesn't it work if you share /var/lib/nfs/* (containing etab, rmtab, sm,  
> sm.bak, state, xtab)?

Not reliably.  You're left with a single point of failure, for one
thing.  You also have races between one server permitting a mount and
others knowing that the mount has been allowed, which can confuse
clients.

	<b


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Re: NFS & Clustering

[Ragnar Kjørstad]

On Wed, Sep 04, 2002 at 09:40:08AM -0700, Bryan O'Sullivan wrote:
> On Wed, 2002-09-04 at 09:24, Emanuel Quass wrote:
>=20
> > but doesn't it work if you share /var/lib/nfs/* (containing etab, rmt=
ab, sm, =20
> > sm.bak, state, xtab)?
>=20
> Not reliably.  You're left with a single point of failure, for one
> thing.  You also have races between one server permitting a mount and
> others knowing that the mount has been allowed, which can confuse
> clients.

I suppose you're suggesting that the disk with /var/lib/nfs/ is a single
point of failure? Well yes, unless you use a redundant storage-system.


The race-condition is only present when the nfs-service is enabled on
both server at the same time. For active/passive failover you have
software that monitor the health of the the primary-system and the
secondary system is only started up if the primary fails. So, there is
no race.



--=20
Ragnar Kj=F8rstad


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