> On Feb 18, 2016, at 1:32 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>
> On Thu, Feb 18, 2016 at 9:14 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>>
>> On Wed, Feb 17, 2016 at 06:55:43PM -0500, Trond Myklebust wrote:
>>> On Wed, Feb 17, 2016 at 5:52 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>>
>>>>> On Feb 17, 2016, at 5:35 PM, Adamson, Andy <William.Adamson@xxxxxxxxxx> wrote:
>>>>> The fs_locations would need to be requested by the client. I guess we reqest them at every mountâ€Ķ.
>>>>
>>>> Yep, and fetch them again every so often. There's no real
>>>> cache coherency protocol for this information. (That's
>>>> where a pNFS layout might be more valuable).
>>>
>>> If your goal is to do session trunking, you only really need to check
>>> the fs_locations attribute on the root file system. (so
>>> GETROOTFH+GETATTR(fs_locations)). That's the natural place for a
>>> server to advertise its full set of IP addresses, and the session
>>> trunking protocol itself will allow you to winnow out any that might
>>> belong to a replica server.
>>
>> I worry that round-robin could behave really badly if the client's path
>> to the two IP addresses have different performance characteristics. But
>> a server should probably still be allowed to advertise those as replicas
>> (e.g. maybe a slower interface is usable as a fallback?).
>>
>> So maybe we should be careful about making this automatic. Unless the
>> load-balancing is a little smarter than pure round robin. Or unless we
>> can get some more fine-grained information (maybe someone could use
>> fs_location_info's preference information for this?).
>
> The multipath policy is pluggable. If you need something more clever
> than round robin, then feel free to play. However do note that for
> pNFS multipathing, both the files and flexfiles specs are clear that
> you should not mix slow and fast transports. I imagine you probably
> want to do the same for fs_locations.
>
> As for fs_locations_info, please see FSLI4BX_(READ|WRITE)(RANK|ORDER).
OK. I’m testing session trunking using new multiple hostname mount options. I’ll submit another RFC patchset.
Then, caveat patchset response, I’ll switch from the multiple hostname mount options to fs_locations_info
—>Andy
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