[gpfsug-discuss] AFM with clones
Venkateswara R Puvvada
vpuvvada at in.ibm.com
Wed May 2 18:48:01 BST 2018
>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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