Differences in memory handling on systems with/out cache drives

Karli Sjöberg Karli.Sjoberg at slu.se
Wed Nov 5 08:44:53 UTC 2014

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

What´s your take on this? Are we hitting bug: 187594 perhaps? How can we


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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