[gpfsug-discuss] AFM misunderstanding

[Mark Bush]

I think I was missing a key piece in that I thought that just doing a mmafmctl fs1 prefetch –j cache would start grabbing everything (data and metadata) but it appears that the –list-file myfiles.txt is the trigger for the prefetch to work properly.  I mistakenly assumed that omitting the –list-file switch would prefetch all the data in the fileset.

From: <gpfsug-discuss-bounces at spectrumscale.org> on behalf of Venkateswara R Puvvada <vpuvvada at in.ibm.com>
Reply-To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: Thursday, April 6, 2017 at 5:45 AM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: Re: [gpfsug-discuss] AFM misunderstanding

Could you explain  "bits of actual file"  mentioned below ?  Prefetch with –metadata-onlypulls 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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