linux-kernel - Re: raid1 with nbd member hangs MD on SLES10 and RHEL5

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Date:	Thu, 14 Jun 2007 21:10:46 -0400
From:	"Mike Snitzer" <snitzer@...il.com>
To:	"Paul Clements" <paul.clements@...eleye.com>
Cc:	"Bill Davidsen" <davidsen@....com>, "Neil Brown" <neilb@...e.de>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
	nbd-general@...ts.sourceforge.net,
	"Herbert Xu" <herbert@...dor.apana.org.au>
Subject: Re: raid1 with nbd member hangs MD on SLES10 and RHEL5

On 6/14/07, Paul Clements <paul.clements@...eleye.com> wrote:
> Mike Snitzer wrote:
>
> > Here are the steps to reproduce reliably on SLES10 SP1:
> > 1) establish a raid1 mirror (md0) using one local member (sdc1) and
> > one remote member (nbd0)
> > 2) power off the remote machine, whereby severing nbd0's connection
> > 3) perform IO to the filesystem that is on the md0 device to enduce
> > the MD layer to mark the nbd device as "faulty"
> > 4) cat /proc/mdstat hangs, sysrq trace was collected
>
> That's working as designed. NBD works over TCP. You're going to have to
> wait for TCP to time out before an error occurs. Until then I/O will hang.

With kernel.org 2.6.15.7 (uni-processor) I've not seen NBD hang in the
kernel like I am with RHEL5 and SLES10.  This hang (tcp timeout) is
indefinite oh RHEL5 and ~5min on SLES10.

Should/can I be playing with TCP timeout values?  Why was this not a
concern with kernel.org 2.6.15.7; I was able to "feel" the nbd
connection break immediately; no MD superblock update hangs, no
longwinded (or indefinite) TCP timeout.

regards,
Mike
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