Comment # 7 on bug 906686 from Neil Brown

I tried running trinity.
I do get lots of processes stuck in 'D' state with symptoms similar to what you
report, but it always clears eventually.

Looking in /proc/meminfo, Writeback is high and slowly decreases.   Once it
gets lot, everything starts moving again.
This is quite normal for NFS.  If you write fast than the connection to the NFS
server will allow (and trinity writes quite a lot to the log files), it will
block from time to time while data flushes out.

However long did it remain blocked for - do you remember?
If you can conveniently run it again, can you check Writeback in /proc/meminfo
when it locks up and see if it is decreasing, and what happens when it reaches
a small number?