[email protected]
[Top] [All Lists]

Re: [zfs-discuss] slow ls or slow zfs

Subject: Re: [zfs-discuss] slow ls or slow zfs
From: Richard Elling
Date: Mon, 29 Jun 2009 09:42:19 -0700
NightBird wrote:
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 Friesenhahn
[email protected],
GraphicsMagick Maintainer,
zfs-discuss mailing list
[email protected]

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.
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

This is a slow disk.  Put your efforts here.

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 
         Cache Miss Ratio:     25%       51106830       [Undefined State for 
         REAL Hit Ratio:       73%       146091795      [MRU/MFU Hits Only]

         Data Demand   Efficiency:    94%
         Data Prefetch Efficiency:    15%

          Anon:                       --%        Counter Rolled.

That is interesting... but only from a developer standpoint.

          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?
Caching isn't your problem, though adding memory may hide the
real problem for a while.  You need faster disk.
-- richard

zfs-discuss mailing list
[email protected]

<Prev in Thread] Current Thread [Next in Thread>