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Re: a simple and scalable pNFS block layout server

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: a simple and scalable pNFS block layout server
From: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
Date: Tue, 6 Jan 2015 10:37:08 -0800
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, linux-nfs@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Weston Andros Adamson <dros@xxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150106175611.GA16413@xxxxxx>
References: <1420561721-9150-1-git-send-email-hch@xxxxxx> <20150106173222.GF12067@xxxxxxxxxxxx> <20150106175611.GA16413@xxxxxx>
On Tue, 6 Jan 2015 18:56:11 +0100
Christoph Hellwig <hch@xxxxxx> 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.  AdditÑonally 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@xxxxxxxxxxxxxxx>

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