Date: Tue, 07 Feb 2012 14:36:20 +0600 From: "Eugene M. Zheganin" <emz@norma.perm.ru> To: freebsd-stable <freebsd-stable@freebsd.org> Subject: zfs arc and amount of wired memory Message-ID: <4F30E284.8080905@norma.perm.ru>
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Hi. 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: ===Cut=== 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 ===Cut=== At the same time I have 3500 megs in wired state: ===Cut=== Mem: 237M Active, 36M Inact, 3502M Wired, 78M Cache, 432K Buf, 37M Free ===Cut=== First question - what is the actual size of ARC, and how can it be determined ? Solaris version of the script is more comprehensive (ran on Solaris): ===Cut=== ARC Size: 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) ===Cut=== The arcstat script makes me think that the ARC size is about 380 megs indeed: ===Cut=== Time read miss miss% dmis dm% pmis pm% mmis mm% size tsize 14:33:35 170M 7466K 4 7466K 4 192 78 793K 3 380M 380M ===Cut=== 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. Thanks. Eugene.
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