----- "Richard Thomas" <[email protected]> wrote: > I couldn't find an answer to this, possibly because it would be a > retarded thing to do but I was just wondering... > > Say you had mirrored (say hardware) RAID with two drives. Reboot the > system with one drive unplugged, make some changes then reboot with > the > other unplugged (and the unplugged one plugged back in), make some > different changes then reboot with both drives plugged back in, what > is > the expected outcome (or is it controller dependent).
In clustered filesystems, this is referred to as split brain. It is why most clustered filesystems want you to have 3 machines minimum. For clustered systems, consider 3 machines and each can talk to the other 2. If one drops off line, the 2 still able to talk can be authoritative. The one that can not talk to any of the others knows it is the one that is isolated and shouldn't respond to filesystem requests. When it can reconnect it can then get updated and reconnect. If you have 2 machines, you can not determine if the other machine is dead or the network is down locally or remotely. The problem you introduce that isn't covered in most failover problems is the idea of rebooting to make the changes. If you hotswap out a drive the machine knows the drive was removed and when it returns it knows to rebuild. You don't have a condition of 2 drives in "current" condition and needing the other to be rebuilt. Most likely the solution would be to pick on to be rebuilt from and do it at the bios level. Otherwise boot from the drive you wish to be correct and then introduce the redundant drive after the controller has established a authoritative drive for the mirror to rebuild against. -- Steven Critchfield [email protected] -- You received this message because you are subscribed to the Google Groups "NLUG" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nlug-talk?hl=en
