Re: a simple and scalable pNFS block layout server

Jeff Layton
2015-01-06T18:37:17Z

On Tue, 6 Jan 2015 18:56:11 +0100
Christoph Hellwig <hch@lst.de> wrote:

> On Tue, Jan 06, 2015 at 12:32:22PM -0500, J. Bruce Fields wrote:
> > - do we have evidence that this is useful in its current form?
>
> What is your threshold for usefulness? It passes xfstests fine, and
> shows linear scalability with multiple clients that each have 10GB
> links.
>
> > - any advice on testing? Is there was some simple virtual setup
> > that would allow any loser with no special hardware (e.g., me)
> > to check whether they've broken the block server?
>
> Run two kvm VMs that share the same disk. Create an XFS filesystem
> on the MDS, and export it. If the client has blkmapd running (on Debian
> it needs to be started manually) it will use pNFS for accessing the
> filesystem. Verify that using the per-operation counters in
> /proc/self/mounstats. Repeat with additional clients as nessecary.
>
> Alternatively set up a simple iSCSI target using tgt or lio and
> connect to it from multiple clients.
>
> > - any debugging advice? E.g., have you checked if current
> > wireshark can handle the MDS traffic?
>
> The wireshare version I've used decoded the generic pNFS operations
> fine, but just dumps the layout specifics as hex data.
>
> Enable the trace points added in this series, they track all stateid
> interactions in the server. Additіonally the pnfs debug printks on
> client and server dump a lot of information.

The wireshark decoder really only handles files layouts right now. Dros
has some patches to add flexfiles support too (once the spec is a bit
more finalized) and at that point it shouldn't be too hard to fix it to
handle block layout as well.

--
Jeff Layton <jlayton@primarydata.com>