[Lustre-discuss] Modifying Lustre network (good practices)

[Andreas Dilger]

You should really be using the LNET Self Test (LST) to do network  
testing. You can do this without changing the Lustre config at all.

Cheers, Andreas

On 2010-05-20, at 8:43, "Brian J. Murrell" <Brian.Murrell at oracle.com>  
wrote:

> On Thu, 2010-05-20 at 16:27 +0200, Olivier Hargoaa wrote:
>>
>> On Lustre we get poor read performances
>> and good write performances so we decide to modify Lustre network in
>> order to see if problems comes from network layer.
>
> Without having any other information other than your statement that
> "performance is good in one direction but not the other" I wonder why
> you consider the network as being the most likely candidate as a  
> culprit
> for this problem.  I haven't come across very many networks that
> (weren't designed to be and yet) are fast in one direction and slow in
> the other.
>
>> Therefore, we'll perform the following steps: we will umount the
>> filesystem, reformat the mgs, change lnet options in modprobe file,
>> start new mgs server, and finally modify our ost and mdt with
>> tunefs.lustre with failover and mgs new nids using "--erase-params"  
>> and
>> "--writeconf" options.
>
> Sounds like a lot of rigmarole to test something that I would consider
> to be of low probability (given the brief amount of information you  
> have
> provided).  But even if I did suspect the network were slow in only  
> one
> direction, before I started mucking with reconfiguring Lustre for
> different networks, I would do some basic network throughput testing  
> to
> verify my hypothesis and adjust the probability of the network being  
> the
> problem accordingly.
>
> Did you do any hardware profiling (i.e. using the lustre-iokit) before
> deploying Lustre on this hardware?  We always recommend profiling the
> hardware for exactly this reason: explaining performance problems.
>
> Unfortunately, now that you have data on the hardware, it's much more
> difficult to profile the hardware because to do it properly, you  
> need to
> be able to write to the disks.
>
> b.
>
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