Re: [Qemu-devel] drive-mirroring to nbd is failing with multiple parallel jobs (qemu 2.9 -> 2.11)

[Wouter Verhelst <w@uter.be>]

Hi Eric,

On Wed, Feb 14, 2018 at 09:11:02AM -0600, Eric Blake wrote:
[NBD and keepalive]
> This is more food for thought on whether it even makes sense for NBD to
> worry about assisting in keepalive matters, or whether it would just be
> bloating the protocol.

I'm currently leaning towards the latter. I don't think it makes (much)
sense to run NBD over an unreliable transport. It uses TCP specifically
to not have to worry about that, under the expectation that it won't
break except in unusual circumstances; if you break that expectation, I
think it's not unfair to say "well, then you get to keep both pieces".

We already set the SO_KEEPALIVE socket option (at least nbd-server does;
don't know about qemu) to make the kernel send out TCP-level keepalive
probes. This happens only after two hours (by default), but it's
something you can configure on your system if you need it to be lower.

Having said that, I can always be convinced otherwise by good arguments
:-)

-- 
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