ZFS Tuning - arc_summary.pl

[jhell]

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On Mon, 29 Mar 2010 10:43, Barry Pederson wrote:
In Message-Id: <4BB0BC7C.3000801 at barryp.org>

> I've been using the arc_summary.pl script from here:
>
> http://jhell.googlecode.com/svn/base/head/scripts/zfs/arc_summary/arc_summary.pl
>
> and noticed some odd numbers, with the ARC Current Size being larger than the 
> Max Size, and the breakdown adding up to less than the current size as shown 
> below
>
> --------
> ARC Size:
>        Current Size:                           992.71M (arcsize)
>        Target Size: (Adaptive)                 512.00M (c)
>        Min Size (Hard Limit):                  81.82M (arc_min)
>        Max Size (Hard Limit):                  512.00M (arc_max)
>
> ARC Size Breakdown:
>        Recently Used Cache Size:       99.84%  511.18M (p)
>        Frequently Used Cache Size:     0.16%   0.82M (c-p)
> --------
>
>
> From another thread I saw, it sounds like arc_max isn't really
> a "Hard Limit" but rather some kind of high water mark.  If that's
> the case then I wonder if this might make more sense....
>
>
>
> ---------
> --- arc_summary.pl.original     2010-02-25 19:23:13.000000000 -0600
> +++ arc_summary.pl      2010-03-29 09:32:28.000000000 -0500
> @@ -121,20 +121,20 @@
>
> my $arc_size = ${Kstat}->{zfs}->{0}->{arcstats}->{size};
> my $arc_size_MiB = ($arc_size / 1048576);
> -my $mfu_size = $target_size - $mru_size;
> +my $mfu_size = $arc_size - $mru_size;
> my $mfu_size_MiB = ($mfu_size / 1048576);
> -my $mru_perc = 100*($mru_size / $target_size);
> -my $mfu_perc = 100*($mfu_size / $target_size);
> +my $mru_perc = 100*($mru_size / $arc_size);
> +my $mfu_perc = 100*($mfu_size / $arc_size);
>
> print "ARC Size:\n";
> printf("\tCurrent Size:\t\t\t\t%0.2fM (arcsize)\n", $arc_size_MiB);
> printf("\tTarget Size: (Adaptive)\t\t\t%0.2fM (c)\n", $target_size_MiB);
> printf("\tMin Size (Hard Limit):\t\t\t%0.2fM (arc_min)\n", 
> $arc_min_size_MiB);
> -printf("\tMax Size (Hard Limit):\t\t\t%0.2fM (arc_max)\n", 
> $arc_max_size_MiB);
> +printf("\tMax Size             :\t\t\t%0.2fM (arc_max)\n", 
> $arc_max_size_MiB);
>
> print "\nARC Size Breakdown:\n";
> printf("\tRecently Used Cache Size:\t%0.2f%%\t%0.2fM (p)\n", $mru_perc, 
> $mru_size_MiB);
> -printf("\tFrequently Used Cache Size:\t%0.2f%%\t%0.2fM (c-p)\n", $mfu_perc, 
> $mfu_size_MiB);
> +printf("\tFrequently Used Cache Size:\t%0.2f%%\t%0.2fM (arcsize-p)\n", 
> $mfu_perc, $mfu_size_MiB);
> print "\n";
>
> ### ARC Efficency ###
>
> -----------
>
>
> Giving something like this...
>
> --------
> ARC Size:
>        Current Size:                           992.88M (arcsize)
>        Target Size: (Adaptive)                 512.00M (c)
>        Min Size (Hard Limit):                  81.82M (arc_min)
>        Max Size             :                  512.00M (arc_max)
>
> ARC Size Breakdown:
>        Recently Used Cache Size:       51.48%  511.18M (p)
>        Frequently Used Cache Size:     48.52%  481.70M (arcsize-p)
> --------
>
> 	Barry
>

Barry,

What branch and revision was this run on ?

I need the above information because the output above just does not match 
up quite as it should and I want to investigate when, where & why as I 
believe something else is going on here that is not on the behalf of 
arc_summary.pl.

Or if you could provide me personally with the full output of the script 
from the downloads section "just to be sure" in an attachment that would 
work as well.

Thanks.

- -- 

  jhell

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