Problem: you see constant high CPU usage on the NetApp, and some of the Linux clients become sluggish, primarily in terms of I/O
1) If iostat is not already on the clients, install the sysstat utilities.
2) On each client mounting from the filer, or on a representative sample of the clients, run iostat with -n so that it shows NFS-related statistics. The following
command will run iostat every 5 seconds and show NFS stats in a nicely tabulated output:
# iostat -nh 5
3) Notice which client exhibits the most NFS operations per second, and correlate it with the NFS volume on that client which shows the most NFS reads and/or writes per second.
At this point you found the most likely culprit in terms of sending NFS traffic to the filer (there could be several client machines in this position, for example if they are part of a cluster).
5) If not already installed, download and install lsof.
6) Run lsof on the client(s) discovered in step 4, and grep for the directory representing the mount point of the NFS volume with the most reads and/or writes. For example:
# lsof | grep /var/log
This will show you, among other things, which processes are accessing which files under that directory. Usually something will jump out at you in terms of things that are going on outside of the ordinary. In my case, it was logrotate kicking off from a daily cron and compressing a huge log file -- since the log file was on a volume NFS-mounted from the filer, this caused the filer to do extra work, hence its increased CPU usage.
That's about it. Of courser these steps can be refined/modified/added to -- but even in this simple form, they can help you pinpoint NFS issues fairly quickly.