[gpfsug-discuss] AFM misunderstanding

[Venkateswara R Puvvada]

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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