[gpfsug-discuss] AFM with clones

[Venkateswara R Puvvada]

>What I’m not clear on is what happens if we update a clone file at home? 
I know AFM is supposed to only transfer the exact bytes updated, does this 
work with clones? i.e. at home do we just get the bytes updated in the 
>copy-on-write clone, or do we accidentally end up shipping the whole file 
back?

IW mode revalidation detects that file is changed at home, all data blocks 
are cleared (punches the hole)  and the next read pulls whole file from 
the home.

~Venkat (vpuvvada at in.ibm.com)



From:   "Simon Thompson (IT Research Support)" <S.J.Thompson at bham.ac.uk>
To:     "gpfsug-discuss at spectrumscale.org" 
<gpfsug-discuss at spectrumscale.org>
Date:   05/02/2018 05:55 PM
Subject:        [gpfsug-discuss] AFM with clones
Sent by:        gpfsug-discuss-bounces at spectrumscale.org



Hi,
 
We are looking at providing an AFM cache of a home which has a number of 
cloned files. From the docs:
https://www.ibm.com/support/knowledgecenter/en/STXKQY_5.0.0/com.ibm.spectrum.scale.v5r00.doc/bl1ins_afmandafmdrlimitations.htm
 
·         We can see that “The mmclone command is not supported on AFM 
cache and AFM DR primary filesets. Clones created at home for AFM filesets 
are treated as separate files in the cache.”
 
So it’s no surprise that when we pre-cache the files, they space consumed 
is different.
 
What I’m not clear on is what happens if we update a clone file at home? I 
know AFM is supposed to only transfer the exact bytes updated, does this 
work with clones? i.e. at home do we just get the bytes updated in the 
copy-on-write clone, or do we accidentally end up shipping the whole file 
back?
 
(note we are using IW mode)
 
Thanks
 
Simon_______________________________________________
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