[gpfsug-discuss] AFM prefetch and eviction policy question

Chris Kempin quixote at us.ibm.com
Fri Jun 21 13:06:35 BST 2019


Ryan:

1) You will need to just regularly run a prefetch to bring over the latest 
files .. you could either just run it regularly on the cache  ( probably 
using the --directory flag to scan the whole fileset for uncached files ) 
or, with a little bit of scripting,  you might be able to drive the 
prefetch from home if you know what files have been created/changed by 
shipping over to the cache a list of files to prefetch and have something 
prefetch that list when it arrives. 

2) As to eviction, just set afmEnableAutoEviction=no and don't evict. is 
there a storage constraint on the cache that would force you to evict?

I was using AFM in a more interactive application, with many small files 
and performance was not an issue in terms of "fast" access to files, but 
things to consider
What  is the network latency between home and cache? 
How big are the files you are dealing with? If you have very large files, 
you may want multiple gateways so they can fetch in parallel.
How much change is there in the files? 
How many new/changed files a day are we talking about?
Are existing files fairly stable? 



Regards,
Chris

Chris Kempin
IBM Cloud - Site Reliability Engineering






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