zfs arc and amount of wired memory
Eugene M. Zheganin
emz at norma.perm.ru
Tue Feb 7 08:36:38 UTC 2012
I have a server with 9.0/amd64 and 4 Gigs of RAM.
Today's questions are about the amount of memory in 'wired' state and
the ARC size.
If I use the script from http://wiki.freebsd.org/ZFSTuningGuide , it says:
ARC Size: 12.50% 363.14 MiB
Target Size: (Adaptive) 12.50% 363.18 MiB
Min Size (Hard Limit): 12.50% 363.18 MiB
Max Size (High Water): 8:1 2.84 GiB
At the same time I have 3500 megs in wired state:
Mem: 237M Active, 36M Inact, 3502M Wired, 78M Cache, 432K Buf, 37M Free
First question - what is the actual size of ARC, and how can it be
Solaris version of the script is more comprehensive (ran on Solaris):
Current Size: 6457 MB (arcsize)
Target Size (Adaptive): 6457 MB (c)
Min Size (Hard Limit): 2941 MB (zfs_arc_min)
Max Size (Hard Limit): 23534 MB (zfs_arc_max)
The arcstat script makes me think that the ARC size is about 380 megs
Time read miss miss% dmis dm% pmis pm% mmis mm%
14:33:35 170M 7466K 4 7466K 4 192 78 793K 3
Second question: if the size is 363 Megs, why do I have 3500 Megs in
wired state? From my experience this is directly related to the zfs, but
380 megs its like about ten times smaller than 3600 megs. At the same
time I have like 700 Megs in swap, so my guess - zfs isn't freeing
memory for current needs that easily.
Yeah, I can tune it down, but I just would like to know what is
happening on an untuned machine.
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