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mount -t nfs qnap:/share/MD0_DATA/disk1 /whatever -o rsize=BLKSIZ,wsize=BLKSIZ,intr,soft,proto=tcp
then try again using with
dd if=/dev/zero of=/mnt/mynfs/test.dd bs=BLKSIZ
where BLKSIZ is whatever is defined in /usr/include/nfsd/const.h
if in doubt, set BLKSIZ=8192
thing is the TCP block size in Linux Kernels >= 2.4 is 32K, NFS version 2
has 8K defined and in NFS version 3 it is up to the server.
You may consider to drop the block size altogether (rzise,wsize &dd).
I've heard about some issues w/ Ubuntu mount.nfs but I am no Ubuntu expert. Sorry.
I found that with sync writes (client side, ie dd -oflags=sync), nfs is not blocking indefinitely anymore.
But there is no mention of this anywhere in nfs documentations.
Also, the error is reported long after I unplug the cable (up to 15 minutes), but if I unplug the cable 10s, then plug it again, the error is reported just there.
And I would prefer to use async writes so I am still open to suggestions.
Last edited by contremaitre; 01-29-2010 at 03:00 AM.
We had the same problem here but after two days investigating it it seems we found an explanation for this. The default protocol for NFS clients is TCP which seems to set its own timeout value. If you use UDP as protocol NFS clients will consider the "timeo" parameter timeout value. After unplugging the network cable the client program will stop after exhausting the local buffer and the timeout time.
I am using UDP but nfs is still blocking.
It seems it depends if the local buffer is full or not.
If I open my files with the SYNC option, then the local buffer will never grow, and the timeout value will be respected.
Otherwise, it never times out.