[stgt] help tgt segfault

FUJITA Tomonori fujita.tomonori at lab.ntt.co.jp
Tue Feb 3 11:52:52 CET 2009

On Tue, 03 Feb 2009 11:46:35 +0100
Tomasz Chmielewski <mangoo at wpkg.org> wrote:

> FUJITA Tomonori schrieb:
> (...)
> >>> 2) you use slow network in this configuration, as you said before?
> >> Yes.
> >> Slow connection is just 5 kB/s in both directions.
> >> It's easy to reproduce the problem this way.
> >> Slow link is the third target above.
> > 
> > So the connections between the target box and are slow
> > while the connections between the target box and is
> > not slow.
> > 
> > Right?
> Yes, it is correct.
> But I'm sure the same will happen with only one target connected (using 
> a slow link).

OK, I guess that I need to see if I can reproduce it.

Is there a good way to emulate a slow link?

> >>> 3) All your bug reports about this problem happened in this
> >>> configuration? If not, please tell me about the other configuration.
> >> In "real life" it happens under slightly different (more complex, harder to set up) conditions:
> >> - tgtd uses DRBD resource as the block device (backing store)
> >> - link is about 100 kB/s (writes; DRBD replication over a slow internet connection) and fast local HDD IO (reads)
> >> - when DRBD exchanges bitmaps with the remote peer, it suspends IO for several seconds
> > 
> > The problem might be related with TMF.
> > 
> > 
> >> - more targets configured, more initiators connected
> > 
> > Hmm, just with lots of initiators? Even with decent link speed and no
> > suspended I/Os?
> _And_ with DRBD and slow link.
> With lots of initiators and decent speed link, no suspended IOs, it 
> behaves stable.

Ok, so all the cases are with 'DRBD and slow link.

> > I'm not sure about what 'more targets configured' mean.
> I mean that "tgtadm --op show --mode target" will output 40-50 targets.
> 4-5 initiators connected to each target.
> But I think it's not relevant, as these segfaults don't relate to the
> number of initiators or targets.

Yes, it's not related. Please start a new thread about this. Probably,
it's easier to fix this.
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