[Pvfs2-users] Problems with varstrip distribution

[Murali Vilayannur]

Hi Juan,
We had never tested varstrip placement with xattrs... Clearly you just
hit upon a bug that I knew was waiting to happen all this while but
did not get to fixing it... :(
Can you try the attached patch against pvfs-2.6.* and see if it works?
You still cannot control which specific I/O node a file will be
created since the
varstrip placement is with respect to some ordinal numbering of servers
which can and is typically random :)

Sample invocation of setfattr could be like
% setfattr -n "user.pvfs2.dist_params" -v "strips:0:512;1:1024"
/mnt/pvfs2/testdir/

will take bytes 0-511 on node 0, 511-1535 on node 1 and so on...

Note how fragile the parsing logic and requirement on how the distrib
params are to be constructed. Very sorry about that.. We really should
find a better way for expressing parameters I think...

If you really need very specific server location placement, you have
to checkout Julian's branch from HEAD (kunkel-hint-branch) and figure
out how to invoke PVFS_sys_create() with the hint parameters. NOTE:
You cannot use xattrs (either system or vfs) since noone has done that
yet with Julian's server-placement hint branch yet...should not be too
hard though.

let me know if this patch still does not get things working again..
thanks,
Murali

On 1/12/07, Juan Piernas Canovas <juan.piernascanovas at pnl.gov> wrote:
> Hi folks,
>
> I'm testing PVFS2, and one of the things I want to do is to control in
> which I/O node a specific file will be stored. With the "simple stripe"
> distribution, I can create a directory and specify for it 1 as the
> number of datafiles to be used. The problem is that every file created
> in that directory is stored in a different I/O node in a round-robin
> fashion.
>
> With the varstrip distribution, you can, in theory at least, indicate
> which I/O nodes, and which chunk size in every node, you want to use for
> a file. But this distribution does not work for me. I have tried the
> following:
>
>     $ mkdir testdir
>     $ setfattr -n "user.pvfs2.dist_name" -v "varstrip_dist" testdir
>     $ setfattr -n "user.pvfs2.dist_params" -v "strips:1:512" testdir
>     $ cp somefile testdir
>     cp: writing `testdir/somefile': Unknown error 132
>
> I have also tried to run:
>
>     $ setfattr -n "user.pvfs2.dist_params" -v "1:512" testdir
>
> but the cp command gets the same error.
>
> Any clue? Is there any way to specific where I can store a file in PVFS2?
>
> Thanks in advance,
>
>     Juan.
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