[CentOS] Intermittent NFS problems with NetApp server

Wed Mar 11 21:23:29 UTC 2009
Alfred von Campe <alfred at von-campe.com>

I've been experiencing some intermittent problems accessing at NetApp  
server via NFS and automount.  I'm running CentOS 5.2 (fully updated)  
on all my servers and workstations.  Usually, everything is working  
just fine, when suddenly we get the following error:

   /bin/sh: /home/epd/srcref/swtools/Crontabs/ 
run_release_requests.sh: Permission denied

This is actually an email from cron because we try to run that shell  
script every minute (yes, the crontab entry is * * * * * /home/epd/ 
srcref/swtools/Crontabs/run_release_requests.sh), and /home/epd is an  
automounted directory.  Here is its map entry:

   epd -rw,nointr,rsize=32768,wsize=32768 XXXXXX:/epd

When this is happening, other users can successfully access that  
directory on the server.  The directory is actually mounted  
correctly, and unmounting doesn't fix the issue.  Furthermore, the  
same user that is being denied access, can successfully access that  
directory on a different server.  The problem usually lasts about 20  
minutes and then resolves itself.  We have been pulling our hair out  
trying to debug this problem, because it's intermittent and the debug  
window is fairly short.

Recently we have been getting help from one of the NetApp admins, and  
he ran a command on the NetApp that produced the following warning:

   The TCP receive window advertised by NFS client XXXXXXX is 5888.
   This is less than the recommended value of 32768 bytes.
   You should increase the TCP receive buffer size for NFS on the  

Some googling around got me to check these values for TCP:

   # sysctl net.ipv4.tcp_mem
   net.ipv4.tcp_mem = 98304        131072  196608
   # sysctl net.ipv4.tcp_rmem
   net.ipv4.tcp_rmem = 4096        87380   4194304
   # sysctl net.ipv4.tcp_wmem
   net.ipv4.tcp_wmem = 4096        16384   4194304

So these seem fine to me (i.e., the max is greater than 32768).  Is  
there an NFS (as opposed to TCP) setting I should be tweaking?  Any  
ideas why the NetApp is issuing those warnings?  Any other  
suggestions on how to debug this problem?