Diagnosing Blocked processes from vmstat

 We are on Linux x86-64 using NetAPP Filer NFS. Started noticing vmstat report 2 to 20 blocked processes (b column). Load average on the server is below 7. CPU and Disk Utilization on the filer are about 60%. What else could be the reason for the interruptable blocked processes? My thinking is that the network between the server and the nfs storage. Any easier way to establish it or any other reason I might have missed?

[ordba@db1epiprod2 ~]$ vmstat 3 300

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------

 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st