[lustre-discuss] Virtual servers

[Jon Tegner]

Hi,

I have been playing around with Lustre on virtual servers (mainly with 
the purpose of gaining some experience).

I have three (physical) machines, and each one have a virtual machine on 
them (KVM). On one of the virtual machines there is an MDS and on two of 
them there are OSS:es installed.

The machines are connected over a 10Gbit network (and I have verified 
the network performance - there are some losses going over the "virtual 
layer" but not terribly much).

All system use CentOS-7.3 and Lustre 2.9.0, and I mount the file system 
on one of the physical machines.

I know it is not recommended to use clients on the same machine as the 
servers, but my hypothesis was that this problem should be mitigated (or 
removed altogether) by "confining" the servers in virtual instances.

Anyway, when evaluating the performance (using FIO) I expected to see an 
increased transfer rate when going from one to two simultaneous files in 
the tests, and I do see this, but only for very small file sizes (around 
0.2 GB). On the "non virtual" file systems I have tested the effect of 
increased transfer rate as the number of files are increased is on the 
other hand easily verified.

Question: could this lack of increased performance be an effect of the 
fact that the client sit on the same machine as one of the Lustre 
servers (even though the server is "confined" in a virtual instance)? Or 
could there be some other issues, possibly connected to running the 
servers on virtual machines?

Thanks,

/jon