Hi Bryn. I'm curious about the fencing used with iSCSI - (I've used hacks with iptables before for Linux based iscsi devices). Also, I've been trying to figure out a way to allow all my nodes access to the same filesystem/LUN with separate directories for each one within the same filesystem for simultaneous access. Is this possible or would this be the place to use the SCSI reservations? This is being done strictly for testing. Regards, Wayne. -----Original Message----- From: linux-cluster-bounces@xxxxxxxxxx [mailto:linux-cluster-bounces@xxxxxxxxxx] On Behalf Of Bryn M. Reeves Sent: Tuesday, April 17, 2007 10:23 AM To: linux clustering Subject: Re: GFS over AOE without fencing? -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Kadlecsik Jozsi wrote: >> If you are using GFS on shared storage then you need fencing. Period. >> >> The only way you can guarantee data integrity in this scenario is by >> completely cutting a failed or misbehaving node off from the storage; >> either by power cycling it or having the storage reject its access. >> >> Otherwise, imagine a situation where a node hangs for some reason and is >> ejected from the cluster. At this point none of its locks for the shared >> data are valid anymore. Some time later, the node recovers from the hang >> and begins flushing writes to the storage -> corruption. > > I see - the sentences above make much more clearer why fencing is needed. > Thank you the explanation - and the hint for the possibility to reject > the access at the storage itself! > > Best regards, > Jozsef Hi Jozsef, No problem! For cutting the access off at the storage there is a new fence agent in the cluster CVS called fence_scsi - you can use that if the storage supports SCSI3 reservations. I don't know if that is the case for AOE though. Otherwise you could use a regular network power switch, or maybe cook something up with a custom fencing script (I've used hacks with iptables before for Linux based iscsi devices). Kind regards, Bryn. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iD8DBQFGJNhI6YSQoMYUY94RAsYKAJ42ozE78Nb4mRo/zide7PNsGTTG0ACgiHYi C2n4BK9zij/IzbnmEIFTcZw= =FGan -----END PGP SIGNATURE----- -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
