[gpfsug-discuss] Placement Policy Installation and RDM Considerations

[Marc A Kaplan]

Yes, you can do this.  In release 4.1.1 you can write   SET POOL 'x' 
ACTION(setXattr(...))  FOR FILESET(...) WHERE ...
which looks nicer to some people than   WHERE ( ... ) AND setXattr(...)

Answers:

(1) No need to quiesce.  As the new policy propagates, nodes begin using 
it.   So there can be a transition time when node A may be using the new 
policy but Node B has not started
using it yet.  If that is undesirable, you can quiesce. 

(2) Yes, 1MB is a limit on the total size in bytes of your policy rules. 
Do you have a real need for more? Would you please show us such a 
scenario?  Beware that policy rules take some cpu cycles to evaluate... So 
if for example, if you had several thousand SET POOL rules, you might 
notice some impact to file creation time.

--marc of GPFS



From:   Luke Raimbach <Luke.Raimbach at crick.ac.uk>
   ... 
RULE 'RDMTEST'
     SET POOL 'instruments’
     FOR FILESET
('%GPFSRDM%10.01013%RDM%0ab34906-5357-4ca0-9d19-a470943db30a%RDM%8fc2395d-64c0-4ebd-8c71-0d2d34b3c1c0')
     WHERE SetXattr
('user.rdm.parent','0ab34906-5357-4ca0-9d19-a470943db30a')
     AND SetXattr
 ('user.rdm.ingestor','8fc2395d-64c0-4ebd-8c71-0d2d34b3c1c0')
RULE 'DEFAULT' SET POOL 'data'
   ...
(1) When I install a placement policy into the file system, does the file 
system need to quiesce? My suspicion is yes, because the policy needs to 
be consistent on all nodes performing I/O, but I may be wrong.
  ...
(2) What is the specific limitation for having a policy placement file no 
larger than 1MB?
  ...

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