[Pvfs2-users] I/O server

[Sam Lang]

On Feb 7, 2007, at 10:27 AM, Suneet Chandok wrote:

> Hi,
>
> I have a question related to I/O servers.  I have 24 node cluster  
> with I/O server running on 23 nodes and 1 meta-data server. Is  
> there a way to configure the system so that only limited number I/O  
> servers are active; lets say 2, 4, 8, or 16. Do I need to generate  
> and distribute new configuration files each time I want to increase  
> or reduce I/O servers and also start server again on all the nodes?  
> I need this for tesing OpenMPI with different number of I/O server.
>
> Please let me know if I am not clear.
>

Hi Suneet,

There is an extended attribute that you can use to get the behavior  
you're looking for.  If you create a directory and set  
user.pvfs2.dfile_count to the number of IO servers you want, all  
files in that directory will use that number of servers.  So if you do:

mkdir dirdf6
setfattr -n "user.pvfs2.dfile_count" -v 6 ./dirdf6/

Then files in the dirdf6 directory will use 6 of the IO servers in  
your system.  Note that the servers are chosen in a round-robin  
fashion, starting randomly, so you won't be able to specifically set  
which servers get used.  There are ways to do this in pvfs, but its  
not as easy as setting the extended attribute described above.

Also not that in the case above the directory is on a pvfs mounted  
volume.  If you don't want to go over the VFS (or don't have setfattr  
installed or something), you can use the pvfs2-setxattr tool, but  
you'll need the attached patch to get that to work properly on  
directories.

You can also use the pvfs2-viewdist tool to see what IO servers a  
file will use, by mapping the datafile handles to the IO servers from  
the config file.

-sam

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> -- 
> Suneet Chandok
> Research Assistant
> Parallel Software Technologies Laboratory
> Department of Computer Science
> University of Houston
>
> Cell: 704-248-0718
> Email: schandok at cs.uh.edu
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