NFS performance issue on Xen virtual machine

[CamZie <camzie@xxxxxxxxxxxxxx>]

Hello everyone,

We are using NFS storage mount on our servers and we have noticed the difference with the write performance on different type of machines. Below you will find the results of writing 2000 1 KB test files:

The command we are using to write 1KB test files is the following:

time seq -w 1 2000 | xargs -n1 -I% sh -c 'sudo dd if=/dev/zero of=file.% bs=1KB count=1 oflag=dsync'

Result on a Xen virtual machine, which is slow:

real    1m10.691s

user    0m17.078s

sys     0m46.313s

Result on a physical server, which is 3-4x faster:

real    0m17.284s

user    0m9.524s

sys     0m5.717s

We have also tried to tune some mount settings and no difference with the performance on the virtual machine:

1) The following is the mount option, as you can see "noatime" is set:

rw,noatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=***REMOVED***,local_lock=none,addr=***REMOVED***

2) "async" is also enabled on the NFS exports.

Does anyone have an idea why and how we can improve the write performance? Thanks!