Setup:

server - FreeBSD 8-stable from today.  2 UFS dirs exported via NFS.
client - FreeBSD 8.0-Release.  Running a test php script that copies around 
various files to/from 2 separate NFS mounts.

Situation: 

script is started (forked to do 20 simultaneous runs) and 20 1GB files are 
copied to the NFS dir which works fine.  When it then switches to reading those 
files back and simultaneously writing to the other NFS mount I see a hang of 75 
seconds.  If I do an "ls -l" on the NFS mount it hangs too.  After 75 seconds 
the client has reported:

nfs server 192.168.10.133:/usr/local/export1: not responding
nfs server 192.168.10.133:/usr/local/export1: is alive again
nfs server 192.168.10.133:/usr/local/export1: not responding
nfs server 192.168.10.133:/usr/local/export1: is alive again 

and then things start working again.  The server was originally FreeBSD 
8.0-Release also but was upgraded to the latest stable to see if this issue 
could be avoided.

# nfsstat -s -W -w 1
 GtAttr Lookup Rdlink   Read  Write Rename Access  Rddir
      0      0      0    222    257      0      0      0
      0      0      0    178    135      0      0      0
      0      0      0     85    127      0      0      0
      0      0      0      0      0      0      0      0
      0      0      0      0      0      0      0      0
      0      0      0      0      0      0      0      0
      0      0      0      0      0      0      0      0
      0      0      0      0      0      0      0      0

... for 75 rows of all zeros

      0      0      0    272    266      0      0      0
      0      0      0    167    165      0      0      0

I also tried runs with 15 simultaneous processes and 25.  15 processes gave 
only about a 5 second stall but 25 gave again the same 75 second stall.   

Further, I tested with 2 mounts to the same server but from ZFS filesytems with 
the exact same stall/timeout periods.  So, it doesn't appear to matter what the 
underlying filesystem is - it's something in NFS or networking code.

Any ideas on what's going on here?  What's causing the complete stall period of 
zero NFS activity?   Any flaws with my testing methods?

Thanks for any and all help/ideas.

--Alan






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