[gpfsug-discuss] AFM misunderstanding
Venkateswara R Puvvada
vpuvvada at in.ibm.com
Thu Apr 6 11:45:37 BST 2017
Could you explain "bits of actual file" mentioned below ? Prefetch with
–metadata-only pulls everything (xattrs, ACLs etc..) except data. Doing "
ls –ltrs" shows file allocation size as zero if data prefetch not yet
completed on them.
~Venkat (vpuvvada at in.ibm.com)
From: Mark Bush <Mark.Bush at siriuscom.com>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 04/06/2017 07:24 AM
Subject: [gpfsug-discuss] AFM misunderstanding
Sent by: gpfsug-discuss-bounces at spectrumscale.org
When I setup a AFM relationship (let’s just say I’m doing RO), does
prefetch bring bits of the actual file over to the cache or is it only
ever metadata? I know there is a –metadata-only switch but it appears
that if I try a mmafmctl prefetch operation and then I do a ls –ltrs on
the cache it’s still 0 bytes. I do see the queue increasing when I do a
mmafmctl getstate. I realize that the data truly only flows once the file
is requested (I just do a dd if=mycachedfile of=/dev/null). But this is
just my test env. How to I get the bits to flow before I request them
assuming that I will at some point need them? Or do I just misunderstand
AFM altogether? I’m more used to mirroring so maybe that’s my frame of
reference and it’s not the AFM architecture.
Mark
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