[Pvfs2-developers] Distribution by hostname

[Julian Martin Kunkel]

Hi,
>So I think we're mostly trying to work out what our API should really 
>be, whether we should extend the distro functionality vs. going totally 
>to hints, and if we go to hints what that API should look like, right?
probably the distribution needs a function which initializes/sets the internal 
parameter depending on the string. Maybe another one which fancy writes the 
parameters to a char buffer.

> I'm down with that.  For the record, my concern over strings isn't in
> our processing them - its the users having to muck with them -
> especially when passing numeric data.  I just worry about lots of
> mallocing/string copying blech when all you really want to do is set the
> stripe size to the variable x.
I think extra mallocing is not really necessary only once to generate the 
string which can be generated with snprintf  the string could look 
like "ioservercount=2;ioservers=node1,node4;dist=simplestripe;dist_stripesize=65536"
whereas options without the prefix "dist_" may be processed by code common to 
all distributions. 

I do not see the benefit of putting the responsibility of server mapping to 
the distribution right now (maybe for raid ?). I like outsourced/common 
processing which is done in the create sm right now.

>I personally don't think the environment variable approach is all that 
>useful for PVFS. I believe this because there are only a *very* limited 
>number of cases where it would apply cleanly (e.g. pvfs2-cp) that there 
>isn't another mechanism for doing the same thing (e.g. MPI-IO hints). I 
>think that MPI-IO hints should have some mechanism along those lines, 
>and I wouldn't mind discussing that separately, but that's a different 
>topic.
Ok I think its true that it might not be that useful for the common case and 
that MPI hints should be used. 
I found it useful for testing and experimenting with PVFS and I think its no 
big deal if environment processing will not be added to CVS. I will add the 
functionality fitting to the new hint interface in my branch.

I don't think that I actually might be useful for implementing the new hint 
mechanism because I think you have to revise the code anyway (and it won't be 
so much work I guess, either), but that is no big deal. 

Julian