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Re: [zones-discuss] The quick & dirty guide to zones on iSCSI LUNs

Subject: Re: [zones-discuss] The quick & dirty guide to zones on iSCSI LUNs
From: Ellard Roush
Date: Thu, 03 Apr 2008 10:55:27 -0800
Hi James,

James Carlson wrote:
> Ellard Roush writes:
>> James Carlson wrote:
>>> That point in time is as soon as your application can start.  It need
>>> not have any dependencies at all.
>> Here is the other point that needs to be clarified.
>> This is not an application.
>> Applications do not start until much later.
>> We have to get the cluster formed and cluster services established
>> before applications run.
> We probably have different definitions of that term.  For networking,
> an "application" is something that uses the services provided by a
> transport or (for raw sockets) network layer protocol.
> I'm not talking about user applications; just things that use
> networking services in some way.
OK. Now I understand what you mean.

> Your program (whatever it is) should not need dependencies on
> networking in order to be successful.  As I suggested before, it's
> sometimes helpful to listen to routing sockets (you can get hints
> there about when it might be a good time to shorten a retry timer, and
> thus make your program respond more quickly), but it's not really a
> dependency issue.
>> The internal interfaces that we had to use are not well documented.
>> Your explanation helps understand what is probably going on.
> It's hinted at in the documentation, but not as well-documented as it
> should be.  man -s 3socket connect says:
>      underlying transport provider. Generally, stream sockets can
>      successfully connect() only once. Datagram sockets  can  use
> [..]
>      ECONNREFUSED     The  attempt  to  connect  was   forcefully
>                       rejected.   The   calling   program  should
>                       close(2) the socket descriptor,  and  issue
>                       another  socket(3SOCKET)  call  to obtain a
>                       new descriptor  before  attempting  another
>                       connect() call.
> That "generally" is also true for most unsuccessful connect() calls
> and the advice under ECONNREFUSED is actually true for pretty much all
> failures.  The exceptions are the non-failure "failures" -- EALREADY,
> EINPROGRESS, and EWOULDBLOCK.  I think that issue is what the text is
> trying to dance around.
> You're partly connected (at least bound) after the real failures, and
> getting back to a clean state is easiest just by close() and trying
> again.
> The usual references (Stevens and others) have more detailed
> discussions.  The underlying problem is that for much of the BSD
> world, the code *is* the documentation, so whatever sockets did, well,
> that's what they do.
> (For what it's worth, this isn't even one of the darker corners.  Raw
> socket behavior, for example, varies in mysterious ways across OS
> platforms and even across releases of a given OS.)
Thanks for the explanation. Our Quorum Server uses the
approach that you suggested. We discovered it the hard way.
We are now attempting to use iSCSI devices as quorum devices.
I will share your insight with the iSCSI people.

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