[gpfsug-discuss] AFM over NFS vs GPFS

Dean Hildebrand dhildeb at us.ibm.com
Wed Mar 2 17:23:30 GMT 2016


Hi Luke,

Assuming the network between your clusters is reliable, using GPFS with
SW-mode (also assuming you aren't ever modifying the data on the home
cluster) should work well for you I think.  New files can continue to be
created in the cache even in unmounted state....

Dean
IBM Almaden Research Center




From:	Luke Raimbach <Luke.Raimbach at crick.ac.uk>
To:	gpfsug main discussion list <gpfsug-discuss at gpfsug.org>
Date:	03/01/2016 04:44 AM
Subject:	[gpfsug-discuss] AFM over NFS vs GPFS
Sent by:	gpfsug-discuss-bounces at spectrumscale.org



HI All,

We have two clusters and are using AFM between them to compartmentalise
performance. We have the opportunity to run AFM over GPFS protocol (over IB
verbs), which I would imagine gives much greater performance than trying to
push it over NFS over Ethernet.

We will have a whole raft of instrument ingest filesets in one storage
cluster which are single-writer caches of the final destination in the
analytics cluster. My slight concern with running this relationship over
native GPFS is that if the analytics cluster goes offline (e.g. for
maintenance, etc.), there is an entry in the manual which says:

"In the case of caches based on native GPFS™ protocol, unavailability of
the home file system on the cache cluster puts the caches into unmounted
state. These caches never enter the disconnected state. For AFM filesets
that use GPFS protocol to connect to the home cluster, if the remote mount
becomes unresponsive due to issues at the home cluster not related to
disconnection (such as a deadlock), operations that require remote mount
access such as revalidation or reading un-cached contents also hang until
remote mount becomes available again. One way to continue accessing all
cached contents without disruption is to temporarily disable all the
revalidation intervals until the home mount is accessible again."

What I'm unsure of is whether this applies to single-writer caches as they
(presumably) never do revalidation. We don't want instrument data capture
to be interrupted on our ingest storage cluster if the analytics cluster
goes away.

Is anyone able to clear this up, please?

Cheers,
Luke.

Luke Raimbach​
Senior HPC Data and Storage Systems Engineer,
The Francis Crick Institute,
Gibbs Building,
215 Euston Road,
London NW1 2BE.

E: luke.raimbach at crick.ac.uk
W: www.crick.ac.uk

The Francis Crick Institute Limited is a registered charity in England and
Wales no. 1140062 and a company registered in England and Wales no.
06885462, with its registered office at 215 Euston Road, London NW1 2BE.
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