[gpfsug-discuss] AFM experiences?

Venkateswara R Puvvada vpuvvada at in.ibm.com
Tue Nov 24 02:32:01 GMT 2020


>- Quota management on the home cluster - we need a way of ensuring
>people don't write data to the cache which can't be accomodated on
>home. Probably not insurmountable but needs a bit of thought...

You could set same quotas between cache and home clusters. AFM does not 
support replication of filesystem metadata like quotas, fileset 
configuration etc...

>- It seems inodes on the cache only get freed when they are deleted on
>the cache cluster - not if they get deleted from the home cluster or
>when the blocks are evicted from the cache. Does this become an issue
>in time?

AFM periodically revalidates with home cluster. If the files/dirs were 
already deleted at home cluster, AFM moves them to <fileset path>/.ptrash 
directory at cache cluster during the revalidation. These files can be 
removed manually by user or auto eviction process. If the .ptrash 
directory is not cleaned up on time, it might result into quota issues at 
cache cluster.

~Venkat (vpuvvada at in.ibm.com)



From:   Robert Horton <robert.horton at icr.ac.uk>
To:     "gpfsug-discuss at spectrumscale.org" 
<gpfsug-discuss at spectrumscale.org>
Date:   11/23/2020 08:51 PM
Subject:        [EXTERNAL] [gpfsug-discuss] AFM experiences?
Sent by:        gpfsug-discuss-bounces at spectrumscale.org



Hi all,

We're thinking about deploying AFM and would be interested in hearing
from anyone who has used it in anger - particularly independent writer.

Our scenario is we have a relatively large but slow (mainly because it
is stretched over two sites with a 10G link) cluster for long/medium-
term storage and a smaller but faster cluster for scratch storage in
our HPC system. What we're thinking of doing is using some/all of the
scratch capacity as an IW cache of some/all of the main cluster, the
idea to reduce the need for people to manually move data between the
two.

It seems to generally work as expected in a small test environment,
although we have a few concerns:

- Quota management on the home cluster - we need a way of ensuring
people don't write data to the cache which can't be accomodated on
home. Probably not insurmountable but needs a bit of thought...

- It seems inodes on the cache only get freed when they are deleted on
the cache cluster - not if they get deleted from the home cluster or
when the blocks are evicted from the cache. Does this become an issue
in time?

If anyone has done anything similar I'd be interested to hear how you
got on. It would be intresting to know if you created a cache fileset
for each home fileset or just one for the whole lot, as well as any
other pearls of wisdom you may have to offer.

Thanks!
Rob

-- 
Robert Horton | Research Data Storage Lead
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T +44 (0)20 7153 5350 | E robert.horton at icr.ac.uk | W www.icr.ac.uk |
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