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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt">I think I need some help with GPFS quotas and hard limits vs soft limits + eviction in AFM scenarios. We\u2019ve got a couple of issues:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.5pt">One:<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt">-------<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">We\u2019ve come across a scenario where if a user hits the hard quota while ingesting into cache in an AFM \u201chome to cache\u201d relationship whilst an eviction loop is being triggered, things seem to go wrong \u2013 and
the filesystem runs off into locking up territory. The report I have on the last incident is that a file-set got stuck at 100% (capacity utilisation), the eviction loop either failed or blocked and the IO requests blocked and/or failed (this one I'm a little
fuzzy on). <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">Maybe it isn\u2019t a bug and our guess is that someone on here will probably tell us that the likely \u201cfix\u201d is to right-size our high and low water marks appropriately. We considered a potential bug mechanism or
race condition if the eviction loop uses space in the file-set in the .afm directory \u2013 but I then thought better of it and though \u201c<i>Nah, surely IBM would have thought of that!</i>\u201d.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.5pt">Two:<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt">-------<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">We witness a scenario where AFM doesn't back off if it gets a filesystem full error code when trying to make the cache clean in migrating data to \u201chome\u201d. If this takes a couple of seconds to raise the error
each attempt, gpfs/mmfsd will deplete NFS daemons causing a DoS against the NFS server that is powering the cache/home relationship for the AFM transport.<br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">We had a mental model that AFM cache wouldn\u2019t or shouldn\u2019t overload hard and soft quota as the high and low watermarks for cache eviction policies. I guess in our heads, we\u2019d like caches to also enforce and
respect <i>quotas</i> based on requests received from home. There are probably lots of reasons this doesn\u2019t make sense programmatically, or to the rest of scale \u2013 but it would (seem to us) that it would clean up this problem or at least some of it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">Happy to chat through his further and explain it more if anyone is interested. If there are any AFM users out there, we\u2019d love to hear about how you deal with quotas, hwm/lwm and eviction over-flow scenarios,
if they exist in your environment.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">Thank you as always, list.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt">-jc<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.5pt"><o:p> </o:p></span></p>
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