On Sat, May 06, 2006 at 10:05:35PM -0500, Stanley, Jon wrote: > The question that I have is that there is functionality in the SCSI-3 > spec for Persistent Group Reservations. Basically, what happens is that > each system that wants access to a disk puts a "reservation" and > "registration" on it. A commercial clustering solution (Symantec) uses > this feature in order to do it's I/O fencing. > > The initial reservation on the disk is "Write Exclusive Registrants > Only", meaning that if you are not registered to be on the disk, you > cannot write to it. When the node comes up, upon synchronizing with all > of the other nodes, etc, it puts it's key onto the disk. It can then > write to the disk, without any problem. When the node dies, the > surviving node(s) see that, and eject the dead node, making it > physically impossible to write to the disk. > > This of course requires support from the array to do it (it's a SCSI-3 > standard, but not all arrays implement it), thereby limiting the choice > of storage to mid-to-high-end enterprise arrays. > > The question is why can't we use that as a fence mechanism, and do away > with the hardware poweroff stuff, if the array supports it? Of course > the hardware poweroff stuff could be left in for older/lower end arrays, > etc, but I think that options are a Good Thing(TM). You could definately use persistent reservations to do fencing, we just don't have a fencing agent written for it yet. It's one of those things that no one ever quite gets the time to do. It's something that would be _really_ nice to have and would spare a lot of people a lot of hassle. Dave -- Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
