From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Philipp Reisner To: "Yeary, Mark A." Date: Fri, 1 Apr 2005 08:51:06 +0200 References: <7A74B5DE6E54D849BAF89B9E2945F11B13E42F@MSG00CV01.utad.utoledo.edu> In-Reply-To: <7A74B5DE6E54D849BAF89B9E2945F11B13E42F@MSG00CV01.utad.utoledo.edu> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200504010851.06410.philipp.reisner@linbit.com> Cc: drbd-dev@linbit.com Subject: [Drbd-dev] Re: On the edge... List-Id: Coordination of development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Am Freitag, 1. April 2005 00:09 schrieben Sie: > Dear Philipp, > > This weekend my IBM X445's go online with DRBD 0.7.10. When it has > been online for a week or so and all runs great I will write a page for > your site. I am very nervous as I have almost 39,000 distance learning > course enrollments running on these boxes. I would like to ask you one > more question. Every night I do a dump of all of my course data to a > scsi tape drive. I would like to perform this function on what is > normally my drbd secondary. Is there any reason I cannot shut down > heartbeat on the secondary, shut down all of the secondary ethernet > interfaces, change the secondary drbd drive to primary temporarily, > mount it and dump it to tape? Afterwards I would unmount the drive on > the secondary, return it to secondary status, turn my interfaces back > on, do a "drbdadm up all" and then restart heartbeat? Is this ok as > long as I do not write data to the secondary when I have it mounted? > Thanks for this one last piece of advice before I go live. I'm trying > to use the secondary to capture a snapshot to tape. My primary will > still be running and collecting data but when I put my secondary back > online it should replicate to the primary, right? I have tested this > and it seems to work but I want your advice. If you say, "No ! Don't do > that !" then I won't. > Hmmm.... Well, right it works with drbd-07 ... The former primary increases its connected-count on disconnect, while the other one increases its unconnected-count.=20 On reconnect the all-the-time primary becomes sync-source because the connected-count has a higher priority than the unconnected-count. So for your production system you will go online with, it is ok to do so. It will also work with subsequent drbd-07 releases... One hint: You might use "drbdadm disconnect all" and "drbdadm connect all" on the seondary, instead of shutting down the ethernet interfaces. =2D But let's look at the picture from a more formal point of view: Actually you created a split brain situation, and crate a own version of the data by making it primary temporarily. At reconenct time DRBD should say "We had a split brain situation..." and offer the recovery policies as discussed in item 5 of=20 http://svn.drbd.org/drbd/trunk/ROADMAP . But on the other hand it is a usefull ussage pattern.... But should probabely be a special command for that. Something like "drbdadm snapshot resource" This would be a new state besides primary and secondary. A resource in snapshot state would allow read-only access, on the transition from secondary -> snapshot it would disconnect itself.=20 primary -> snapshot is not allowed. snapshot -> secondary would reconnect the resource, but is only=20 possible if we can claim the device again =3D=3D it is no longer mounted. =2Dphilipp =2D-=20 : Dipl-Ing Philipp Reisner Tel +43-1-8178292-50 : : LINBIT Information Technologies GmbH Fax +43-1-8178292-82 : : Sch=F6nbrunnerstr 244, 1120 Vienna, Austria http://www.linbit.com :