Appalling write speed using NFS

Question

I've set up a NFS share on my Raspberry by installing @nfs-kernel-server@ and configuring the following export:

/media/hdd 192.168.1.0/24(rw,async)

I've mounted the share on a Ubuntu client using

192.168.1.51:/media/hdd /media/myuser/hdd nfs hard,intr,rsize=X,wsize=Y,proto=Z

and tried with several values for X, Y and Z. However, no matter what values I use, copying a large (~8GB) file to the share will start at ~45MB/s for the first ~800MB and suddenly drop to an appalling ~800KB/s and sometimes even freeze. What am I doing wrong? I am using Xbian 1.0 Beta 1.1.

Answer 1

I had the same problem, but with regular dekstop-clients and servers. Turned out NFS gave false reading regarding speed, since it cached a lot and basically said it was done with lots of MB/GB, while it was still copying in the background. This was only notable when copying large files, since the internal cache was exhausted.

First of all, use this command to test the performance:

dd bs=1M count=512 if=/dev/zero of=/media/myuser/hdd/test conv=fdatasync

Second, try using some other protocol. sshfs or just scp is a good indicator of performance-speed.

I also noticed that the default values for rsize,wsize where good engough. Thats not where to start looking.