From owner-freebsd-stable@FreeBSD.ORG  Tue Jan 16 19:34:10 2007
Return-Path: <owner-freebsd-stable@FreeBSD.ORG>
X-Original-To: freebsd-stable@freebsd.org
Delivered-To: freebsd-stable@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
	by hub.freebsd.org (Postfix) with ESMTP id E871F16A407
	for <freebsd-stable@freebsd.org>; Tue, 16 Jan 2007 19:34:10 +0000 (UTC)
	(envelope-from ambrisko@ambrisko.com)
Received: from mail.ambrisko.com (mail.ambrisko.com [64.174.51.43])
	by mx1.freebsd.org (Postfix) with ESMTP id BE8F713C442
	for <freebsd-stable@freebsd.org>; Tue, 16 Jan 2007 19:34:10 +0000 (UTC)
	(envelope-from ambrisko@ambrisko.com)
Received: from server2.ambrisko.com (HELO www.ambrisko.com) ([192.168.1.2])
	by mail.ambrisko.com with ESMTP; 16 Jan 2007 11:30:51 -0800
Received: from ambrisko.com (localhost [127.0.0.1])
	by www.ambrisko.com (8.13.1/8.12.11) with ESMTP id l0GJY1Fs057096;
	Tue, 16 Jan 2007 11:34:01 -0800 (PST)
	(envelope-from ambrisko@ambrisko.com)
Received: (from ambrisko@localhost)
	by ambrisko.com (8.13.1/8.13.1/Submit) id l0GJY1mh057095;
	Tue, 16 Jan 2007 11:34:01 -0800 (PST) (envelope-from ambrisko)
From: Doug Ambrisko <ambrisko@ambrisko.com>
Message-Id: <200701161934.l0GJY1mh057095@ambrisko.com>
In-Reply-To: <20070116185157.GB97568@xor.obsecurity.org>
To: Kris Kennaway <kris@obsecurity.org>
Date: Tue, 16 Jan 2007 11:34:01 -0800 (PST)
X-Mailer: ELM [version 2.4ME+ PL94b (25)]
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset=US-ASCII
Cc: freebsd-stable@freebsd.org, Scott Oertel <freebsd@scottevil.com>,
	Willem Jan Withagen <wjw@digiware.nl>
Subject: Re: running mksnap_ffs
X-BeenThere: freebsd-stable@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Production branch of FreeBSD source code <freebsd-stable.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>, 
	<mailto:freebsd-stable-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-stable>
List-Post: <mailto:freebsd-stable@freebsd.org>
List-Help: <mailto:freebsd-stable-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>,
	<mailto:freebsd-stable-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 16 Jan 2007 19:34:11 -0000

Kris Kennaway writes:
| On Tue, Jan 16, 2007 at 10:13:57AM -0800, Doug Ambrisko wrote:
|
| > FWIW, with this patch I find making snap-shots a lot more reliable:
| >
| > --- sys/ufs/ffs/ffs_snapshot.c.orig Wed Mar 22 09:42:31 2006
| > +++ sys/ufs/ffs/ffs_snapshot.c      Mon Nov 20 14:59:13 2006
| > @@ -282,6 +282,8 @@ restart:
| >             if (error)
| >                     goto out;
| >             bawrite(nbp);
| > +           if (cg % 10 == 0)
| > +                   ffs_syncvnode(vp, MNT_WAIT);
| >     }
| >     /*
| >      * Copy all the cylinder group maps. Although the
| > @@ -303,6 +305,8 @@ restart:
| >                     goto out;
| >             error = cgaccount(cg, vp, nbp, 1);
| >             bawrite(nbp);
| > +           if (cg % 10 == 0)
| > +                   ffs_syncvnode(vp, MNT_WAIT);
| >             if (error)
| >                     goto out;
| >     }
| >
| > or things can get wedged.  We have some other patches as well that might
| > be required.  As a hack on a local server we have been using snap shots
| > to do a "hot" back-up of a data base each morning.  This is based on
| > 6.x.
|
| What do you mean by "get wedged"?  Are you seeing a deadlock, and if
| so then what are the details?  When you say 6.x, do you mean
| up-to-date RELENG_6?  There were various snapshot deadlock fixes
| committed over the past year including some in the past few months.

The file-system would come to a stop, processes stuck on bio, snap-shots
not finishing etc.  This was caused by the system running out of usable
buffers.  The change forces them to be flushed every so often.  This is
independant of locking.  10 might be to aggresive.  Some scaling of
nbuf would probably be better.

Doug A.