linux-kernel - Re: [Scst-devel] Integration of SCST in the mainstream Linux kernel

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Message-Id: <20080206014340X.tomof@acm.org>
Date:	Wed, 6 Feb 2008 01:43:37 +0900
From:	FUJITA Tomonori <tomof@....org>
To:	mangoo@...g.org
Cc:	fujita.tomonori@....ntt.co.jp
Subject: Re: [Scst-devel] Integration of SCST in the mainstream Linux kernel

On Tue, 05 Feb 2008 17:07:07 +0100
Tomasz Chmielewski <mangoo@...g.org> wrote:

> FUJITA Tomonori schrieb:
> > On Tue, 05 Feb 2008 08:14:01 +0100
> > Tomasz Chmielewski <mangoo@...g.org> wrote:
> > 
> >> James Bottomley schrieb:
> >>
> >>> These are both features being independently worked on, are they not?
> >>> Even if they weren't, the combination of the size of SCST in kernel plus
> >>> the problem of having to find a migration path for the current STGT
> >>> users still looks to me to involve the greater amount of work.
> >> I don't want to be mean, but does anyone actually use STGT in
> >> production? Seriously?
> >>
> >> In the latest development version of STGT, it's only possible to stop
> >> the tgtd target daemon using KILL / 9 signal - which also means all
> >> iSCSI initiator connections are corrupted when tgtd target daemon is
> >> started again (kernel upgrade, target daemon upgrade, server reboot etc.).
> > 
> > I don't know what "iSCSI initiator connections are corrupted"
> > mean. But if you reboot a server, how can an iSCSI target
> > implementation keep iSCSI tcp connections?
> 
> The problem with tgtd is that you can't start it (configured) in an
> "atomic" way.
> Usually, one will start tgtd and it's configuration in a script (I 
> replaced some parameters with "..." to make it shorter and more readable):

Thanks for the details. So the way to stop the daemon is not related
with your problem.

It's easily fixable. Can you start a new thread about this on
stgt-devel mailing list? When we agree on the interface to start the
daemon, I'll implement it.


> tgtd
> tgtadm --op new ...
> tgtadm --lld iscsi --op new ...

(snip)

> So the only way to start/restart tgtd reliably is to do hacks which are 
> needed with yet another iSCSI kernel implementation (IET): use iptables.
> 
> iptables <block iSCSI traffic>
> tgtd
> sleep 1
> tgtadm --op new ...
> tgtadm --lld iscsi --op new ...
> iptables <unblock iSCSI traffic>
> 
> 
> A bit ugly, isn't it?
> Having to tinker with a firewall in order to start a daemon is by no 
> means a sign of a well-tested and mature project.
> 
> That's why I asked how many people use stgt in a production environment 
> - James was worried about a potential migration path for current users.

I don't know how many people use stgt in a production environment but
I'm not sure that this problem prevents many people from using it in a
production environment.

You want to reboot a server running target devices while initiators
connect to it. Rebooting the target server behind the initiators
seldom works. System adminstorators in my workplace reboot storage
devices once a year and tell us to shut down the initiator machines
that use them before that.
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