Differences in memory handling on systems with/out cache drives

[Karli Sjöberg]

On Wed, 2014-11-05 at 08:44 +0000, Karli Sjöberg wrote:
> Hey all!
> 
> Still investigating the intermittent lockups we are experiencing on our
> storage systems and have started to compare memory graphs from our
> Graphite monitoring system. What´s interesting about two of our systems
> is that they both have the same amount of RAM; 32 GB. But on one of
> them, I have "zpool remove"'d the cache drives from the pool and have
> been able to study how different their memory graphs now look like.
> 
> Also worth noting is that the cache-less system nearly haven´t swapped
> at all (1112K) since the last stall 20 days ago, while the other system
> has swapped 78 MB during it´s 48 days of uptime.
> 
> I´ve attached both screenshots from the two systems, with- and without
> cache drives, displaying a period of 12 hours.
> 
> What´s most notable are the characteristic cuts that happen on the
> cache-less system when ZFS goes in and evicts blocks from ARC that shows
> as a decrease in "wired" and increase in "free", that just doesn´t
> happen/looks different in the system with cache drive configured in the
> pool.
> 
> What´s your take on this? Are we hitting bug: 187594 perhaps? How can we
> know?
> 
> 
> -- 
> 
> Med Vänliga Hälsningar
> 
> -------------------------------------------------------------------------------
> Karli Sjöberg
> Swedish University of Agricultural Sciences Box 7079 (Visiting Address
> Kronåsvägen 8)
> S-750 07 Uppsala, Sweden
> Phone:  +46-(0)18-67 15 66
> karli.sjoberg at slu.se
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Damnit, the images attached disappeared, here are weblinks for them
instead:

with-l2arc:    http://i.imgur.com/ouNFOvc.png

without-l2arc: http://i.imgur.com/0pBkyOS.png

Sorry about that.


-- 

Med Vänliga Hälsningar

-------------------------------------------------------------------------------
Karli Sjöberg
Swedish University of Agricultural Sciences Box 7079 (Visiting Address
Kronåsvägen 8)
S-750 07 Uppsala, Sweden
Phone:  +46-(0)18-67 15 66
karli.sjoberg at slu.se