[gpfsug-discuss] AFM experiences?

[Flanders, Dean]

Hello Rob,

We looked at AFM years ago for DR, but after reading the bug reports, we avoided it, and also have had seen a case where it had to be removed from one customer, so we have kept things simple. Now looking again a few years later there are still issues, IBM Spectrum Scale Active File Management (AFM) issues which may result in undetected data corruption<https://www.ibm.com/support/pages/ibm-spectrum-scale-active-file-management-afm-issues-which-may-result-undetected-data-corruption>, and that was just my first google hit. We have kept it simple, and use a parallel rsync process with policy engine and can hit wire speed for copying of millions of small files in order to have isolation between the sites at GB/s. I am not saying it is bad, just that it needs an appropriate risk/reward ratio to implement as it increases overall complexity.

Kind regards,

Dean

From: gpfsug-discuss-bounces at spectrumscale.org <gpfsug-discuss-bounces at spectrumscale.org> On Behalf Of Ryan Novosielski
Sent: Monday, November 23, 2020 4:31 PM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: Re: [gpfsug-discuss] AFM experiences?

We use it similar to how you describe it. We now run 5.0.4.1 on the client side (I mean actual client nodes, not the home or cache clusters). Before that, we had reliability problems (failure to cache libraries of programs that were executing, etc.). The storage clusters in our case are 5.0.3-2.3.

We also got bit by the quotas thing. You have to set them the same on both sides, or you will have problems. It seems a little silly that they are not kept in sync by GPFS, but that’s how it is. If memory serves, the result looked like an AFM failure (queue not being cleared), but it turned out to be that the files just could not be written at the home cluster because the user was over quota there. I also think I’ve seen load average increase due to this sort of thing, but I may be mixing that up with another problem scenario.

We monitor via Nagios which I believe monitors using mmafmctl commands. Really can’t think of a single time, apart from the other day, where the queue backed up. The instance the other day only lasted a few minutes (if you suddenly create many small files, like installing new software, it may not catch up instantly).

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On Nov 23, 2020, at 10:19, Robert Horton <robert.horton at icr.ac.uk<mailto:robert.horton at icr.ac.uk>> wrote:
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

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