From owner-freebsd-geom@FreeBSD.ORG Sun Jun 22 19:08:32 2008 Return-Path: Delivered-To: freebsd-geom@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 66949106567D for ; Sun, 22 Jun 2008 19:08:32 +0000 (UTC) (envelope-from gcubfg-freebsd-geom@m.gmane.org) Received: from ciao.gmane.org (main.gmane.org [80.91.229.2]) by mx1.freebsd.org (Postfix) with ESMTP id E912C8FC17 for ; Sun, 22 Jun 2008 19:08:31 +0000 (UTC) (envelope-from gcubfg-freebsd-geom@m.gmane.org) Received: from list by ciao.gmane.org with local (Exim 4.43) id 1KATpw-0004gF-KP for freebsd-geom@freebsd.org; Sun, 22 Jun 2008 17:58:48 +0000 Received: from 78-0-84-134.adsl.net.t-com.hr ([78.0.84.134]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 22 Jun 2008 17:58:48 +0000 Received: from ivoras by 78-0-84-134.adsl.net.t-com.hr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 22 Jun 2008 17:58:48 +0000 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-geom@freebsd.org From: Ivan Voras Date: Sun, 22 Jun 2008 19:58:34 +0200 Lines: 66 Message-ID: References: <0A8C1986-1DC1-4445-9111-0DEDBBCC6847@hmallett.co.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig1504CD62C27849ABF1105167" X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 78-0-84-134.adsl.net.t-com.hr User-Agent: Thunderbird 2.0.0.14 (Windows/20080421) In-Reply-To: <0A8C1986-1DC1-4445-9111-0DEDBBCC6847@hmallett.co.uk> X-Enigmail-Version: 0.95.6 Sender: news Subject: Re: Filesystem replication geom proposal X-BeenThere: freebsd-geom@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: GEOM-specific discussions and implementations List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 22 Jun 2008 19:08:32 -0000 This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig1504CD62C27849ABF1105167 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Hywel Mallett wrote: > FreeBSD doesn't have a defined method of replicating data between two=20 > servers, for HA/DR purposes, similar to Veritas Volume Replicator. Linu= x=20 > has DRDB (http://www.drbd.org/) which isn't quite the same, and someone= =20 > has tried using gmirror and ggate to have a mirror across teo systems, = > but neither of those can cope well with a disconnected network, or a=20 > slow network link. > I was wondering if there would be any interest in creating a new geom=20 > provider to solve this problem. I can see that questions about this=20 > functionality have been asked on the mailing lists before, and I've=20 > drawn up some initial thoughts aand ideas at=20 > http://www.hmallett.co.uk/computing-mainmenu-49/72-computing/124-open-s= ource-replicated-filesystems.html=20 Hmmm. If I understand your proposal, you want to create IO journals on=20 both the master and the slave, then replicate journal data from the=20 master to the slave, then replay the journal on the slave? This looks=20 like a lot of work for something that looks like it could be implemented = by a linked list in the kernel (to achieve aynchronous operation). The DCM looks like an alternative to the above "transactional" method of = replication - it looks like instead of asynchronously replaying the=20 transaction log, you constantly replicate the DCM to the slave (or at=20 least the changed bits), and then the slave asks the server to send the=20 blocks corresponding to what's marked as changed in the DCM, right? Regarding swapping the master/slave roles: I think you need a fsck step=20 somewhere in there, or the same tricks gjournal uses (hooks into UFS)=20 since the file system will be marked dirty if you suddenly stop using=20 it. Also, to manually force the failover, the master needs to umount the = file system, probably with "-f". Will it work? Of course, if you think the things you proposed will solve reliable=20 replication of data across the network, go ahead :) But since=20 ggate+gmirror has already tried to solve this, maybe you'd be interested = in increasing their reliability, as an exercise before trying something=20 from scratch? --------------enig1504CD62C27849ABF1105167 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFIXpLKldnAQVacBcgRAkDWAKCVLdvBBvhXKnCu227t/Rzk9tg6FwCgphKI Kvu6ziF/NbwjFq7juqW/p1s= =5KG3 -----END PGP SIGNATURE----- --------------enig1504CD62C27849ABF1105167--