[gpfsug-discuss] Antwort: [Newsletter] Re: Combine different rules - tip: use mmfind & co; FOR FILESET; FILESET_NAME

[Matthias.Knigge at rohde-schwarz.com]

Thanks for this tip. I will try these commands and give feedback in the 
next week.

Matthias




Von:    "Marc A Kaplan" <makaplan at us.ibm.com>
An:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Datum:  01.11.2017 15:43
Betreff:        [Newsletter] Re: [gpfsug-discuss] Combine different rules 
- tip: use mmfind & co; FOR FILESET; FILESET_NAME
Gesendet von:   gpfsug-discuss-bounces at spectrumscale.org



Thanks Jonathan B for your comments and tips on experience using 
mmapplypolicy and policy rules.  Good to see that some of the features we 
put into the product are actually useful.  

For those not quite as familiar, and have come somewhat later to the game, 
like Matthias K - I have a few remarks and tips that may be helpful:

You can think of and use mmapplypolicy as a fast, parallelized version of 
the classic   `find ... | xargs ... `  pipeline.
In fact we've added some "sample" scripts with options that make this 
easy:

samples/ilm/mmfind  :  "understands" the classic find search arguments as 
well as all the mmapplypolicy options and the recent versions
  also support an -xargs option so you can write the classic pipepline as 
one command:   mmfind ... -xargs ...
 
There are debug/diagnostic options so you can see the underlying GPFS 
commands and policy rules that are generated, so if mmfind doesn't do 
exactly what you were hoping, you can capture the commands and rules that 
it does do and tweak/hack those.

Two of the most crucial and tricky parts of mmfind are available as 
separate scripts that can be used separately:

tr_findToPol.pl :  convert classic options to policy rules.
 
mmxargs :   100% correctly deal with the problem of whitespace and/or 
"special" characters in the pathnames output as file lists by
                       mmapplypolicy.  This is somewhat tricky.  

EVEN IF you've already worked out your own policy rules and use policy 
RULE  ... EXTERNAL ...  EXEC 'myscript'
you may want to use mmxargs or "lift" some of the code there-in -- because 
it is very likely your 'myscript' is not handling the problem of special 
characters correctly.

FILESETs vs POOLs - yes these are "orthogonal" concepts in GPFS (Spectrum 
Scale!)  BUT some customer/admins may choose to direct GPFS to assign to 
POOL based on FILESET using policy rules clauses like:
    FOR FILESET('a_fs', 'b_fs')   /* handy to restrict a rule to one or a 
few filesets */
    WHERE ...   AND (FILESET_NAME LIKE 'xyz_%') AND ...  /*  restrict to 
filesets whose name matches a pattern */

-- marc of GPFS_______________________________________________
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