zfs arc and amount of wired memory

[Andriy Gapon]

on 07/02/2012 10:36 Eugene M. Zheganin said the following:
> 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===

Please try sysutils/zfs-stats; zfs-stats -a output should provide a good
overview of the state and configuration of the system.

> 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.


-- 
Andriy Gapon