[Libguestfs] Thoughts on nbdkit automatic reconnection

[Richard W.M. Jones]

On Wed, Sep 18, 2019 at 01:59:01PM +0100, Richard W.M. Jones wrote:
> We have a running problem with the nbdkit VDDK plugin where the VDDK
> side apparently disconnects or the network connection is interrupted.
> During a virt-v2v conversion this causes the entire operation to fail,
> and since v2v conversions take many hours that's not a happy outcome.
> 
> (Aside: I should say that we see many cases where it's claimed that
> the connection was dropped, but often when we examine them in detail
> the cause is something else.  But it seems like this disconnection
> thing does happen sometimes.)

It turns out in the customer case that led us to talk about this, a
Checkpoint firewall was forcing the VDDK control connection to be
closed after an idle period.  (The VDDK connection as a whole was not
actually idle because data was being copied over the separate data
port, but the firewall did not associate the two ports).  I believe
nbdkit-retry-filter would have helped in this case because reopening
the VDDK connection will reestablish the control/metadata connection,
and therefore I am looking at an implementation now.

Rich.

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