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Re: a simple and scalable pNFS block layout server

To: Jeffrey Layton <jeff.layton@xxxxxxxxxxxxxxx>
Subject: Re: a simple and scalable pNFS block layout server
From: Weston Andros Adamson <dros@xxxxxxxxxxxxxxx>
Date: Tue, 6 Jan 2015 13:39:50 -0500
Cc: Christoph Hellwig <hch@xxxxxx>, "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, linux-nfs list <linux-nfs@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150106103708.70a06aba@xxxxxxxxxxxxxxxxxxxxxxxxx>
References: <1420561721-9150-1-git-send-email-hch@xxxxxx> <20150106173222.GF12067@xxxxxxxxxxxx> <20150106175611.GA16413@xxxxxx> <20150106103708.70a06aba@xxxxxxxxxxxxxxxxxxxxxxxxx>
> On Jan 6, 2015, at 1:37 PM, Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx> wrote:
> 
> 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.

I should be publishing these patches soon. The only holdup is waiting
on the IANA layout type assignment.

-dros

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