Re: [Qemu-devel] [PATCH v3 00/11] NBD reconnect

[Eric Blake]

On 07/03/2018 08:46 AM, Vladimir Sementsov-Ogievskiy wrote:
> Hi all.
>
> before v4 realization, I'd like to discuss some questions.
>
> Our proposal for v4 is the following:
>
> 1. don't reconnect on nbd_open. So, on open we do only one connect 
> attempt, and if it fails, open fails.
> 2. don't configure timeout between attempts. instead do the following:
>      1s timeout, then 2s, then 4, 8, 16, and then always 16 until success
> 3. configure only time, after disconnect, during which requests are 
> paused (and after this time, if not connected, they will return EIO). Or 
> not configure it for now, make a default of 5 minutes.
>
> Any ideas?

I apologize that I haven't had time to review this series closely.  At 
this point, I think it's missed 3.0, and will have to be 3.1 material. 
Your proposal for exponential backoff on reconnect attempts makes sense; 
beyond that, I haven't reviewed closely enough to know if I have other 
suggestions on how many knobs to expose to the user, vs. how much to 
make automatic.

> 09.06.2018 18:32, Vladimir Sementsov-Ogievskiy wrote:
> > Hi all.
> >
> > Here is NBD reconnect.
> > The feature realized inside nbd-client driver and works as follows:
> >
> > There are two parameters: reconnect-attempts and reconnect-timeout.
> > So, we will try to reconnect in case of initial connection failed or
> > in case of connection lost. All current and new io operations will wait
> > until we make reconnect-attempts tries to reconnect. After this, all
> > requests will fail with EIO, but we will continue trying to reconnect.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org