[Pvfs2-users] basic questions about pvfs2

[Sam Lang]

On Jul 5, 2007, at 11:53 PM, xiangyong ouyang wrote:

>
> I'm running MPI-IO program to test the write/read performance with  
> pvfs2 file system on a linux cluster. Here are some questions I'm  
> not clear with.
>
> 1. For a file in pvfs2 file system, from which IO server the pvfs2  
> begin to stripe file data? In another word, how to find the first  
> IO server that starts to stripe this file stored in pvfs2 file system?

The first server a file is striped over is chosen randomly.  A  
development patch has been posted to the developers list that allows  
the first server (and in fact the order of all the servers) to be  
specified to the PVFS_sys_create function.  This support doesn't  
exist in a PVFS released version or MPI-IO at present.

>
> 2. How to change the strip_size? I know we can change the  
> PVFS_DIST_SIMPLE_STRIPE_DEFAULT_STRIP_SIZE value in the source  
> header file: include/pvfs2-dist-simple-stripe.h.  But that requires  
> a re-compilation whenever I change the value. Is there a global  
> environment variable that I can set to change the strip size?

You *should* be able to specify the strip size in the config file:

<Distribution>
	Name simple_stripe
	Param strip_size
	Value 524288
</Distribution>

This should be specified within the <Filesystem> context.

There's a bug in the 2.6.3 release that doesn't allow this to work  
though.  I've attached a patch that you can apply that will fix the bug.

-sam

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>
> thanks!
>
>
> xiangyong ouyang
>
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