> On Fri, 26 Jun 2009, Richard Elling wrote:
>
> >> All the tools I have used show no IO problems. I
> think the problem is
> >> memory but I am unsure on how to troubleshoot it.
> >
> > Look for latency, not bandwidth. iostat will show
> latency at the
> > device level.
>
> Unfortunately, the effect may not be all that obvious
> since the disks
> will only be driven as hard as the slowest disk and
> so the slowest
> disk may not seem much slower.
>
> Bob
> --
> Bob Friesenhahn
> bfrie...@simple.dallas.tx.us,
> http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,
> http://www.GraphicsMagick.org/
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> ss
I checked the output of iostat. svc_t is between 5 and 50, depending on when
data is flushed to the disk (CIFS write pattern). %b is between 10 and 50.
%w is always 0.
Example:
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd27 31.5 127.0 935.9 616.7 0.0 11.9 75.2 0 66
sd28 5.0 0.0 320.0 0.0 0.0 0.1 18.0 0 9
This tells me disks are busy but I do not know what they are doing? are they
spending time seeking, writting or reading?
I also review some ARC stats. Here is the output.
ARC Efficency:
Cache Access Total: 199758875
Cache Hit Ratio: 74% 148652045 [Defined State for
buffer]
Cache Miss Ratio: 25% 51106830 [Undefined State for
Buffer]
REAL Hit Ratio: 73% 146091795 [MRU/MFU Hits Only]
Data Demand Efficiency: 94%
Data Prefetch Efficiency: 15%
CACHE HITS BY CACHE LIST:
Anon: --% Counter Rolled.
Most Recently Used: 22% 33843327 (mru) [
Return Customer ]
Most Frequently Used: 75% 112248468 (mfu) [
Frequent Customer ]
Most Recently Used Ghost: 3% 4833189 (mru_ghost) [
Return Customer Evicted, Now Back ]
Most Frequently Used Ghost: 22% 33831706 (mfu_ghost) [
Frequent Customer Evicted, Now Back ]
It seems to me that mfu_ghost being at 22%, I may need a bigger ARC.
Is ARC also designed to work with large memory foot prints (128GB for example
or higher)? Will it be as efficient?
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