Re: [Nbd] Yet another NBD server out there

[Michal Belczyk <belczyk@...1274...>]

On Sat, Mar 09, 2013 at 02:17:19PM +0100, folkert wrote:
> >   http://code.belo.io/bnbd/
> 
> Some comments: it fails silently. You need to dig in syslog to find out
> it could not write its PID-file. Imho that should be shown on the
> console.

Yeah, perhaps it should, but for now one has to take a look in the logs
or use -d option to make it stay foreground and display the logs on the
console (when specified twice the config file option syslog_priority is
ignored and all logs up to the debug level show up -- see
scripts/bnbd-server.sh).


> It also would just disappear without any messages in syslog.

Now this looks like a bug to me -- could you please file an issue for it
on the project's bitbucket site and provide more details?
Much appreciated!
I think we should discuss this in private as this mailing list is
definitely not the right place to solve any bnbd-server issues...
Thanks!


> Am I right that it only speaks the new protocol?

Indeed.


> > It is a true network _block_ device, not a network _memory_ device as it
> > does not take any advantage of the buffer cache on the data origin
> > server.
> 
> What's the advantage of that?

There are both advantages and disadvantages -- it all depends on the use
case and it all depends on what you expect from a block device...
I do not expect more than the underlying physical device's raw
performance, I do expect that buffer cache flushes on the client side
actually hit at least the underlying device's write cache (nearly sync
writes on the server side), specifically when client-side applications
call fsync(), and I do expect the server not to block for a long
time when the server-side VM will block it while flushing data to disk,
causing clients to time out... which implies nearly-sync writes or
aggressive VM tuning on the server side (reducing caches, forcing more
often data flushes, etc...).

I have never claimed that bnbd-server is a replacement for the original
nbd-server -- they are both two different beasts... and mine is just a
different approach to the whole NBD thing...

-- 
Michal Belczyk Sr.