Hello,
I have a questions with respect to RADOS and RBD and the cluster monitor daemons.
1) Is there any chance that the cluster monitor protocol will be enhanced to work practically with only 2 monitor daemons? I ask since this seems like it would allow a 2 node RBD based device to effectively replace a DRBD based device and yet be much more easily expandable to more nodes than DRBD. Many HA systems (say telco racks) only have two nodes and it seems silly to miss out on the opportunity to be able to use RBD in those systems.
One suggestion I have would be to do this would be to use some of the same techniques that heartbeat uses to determine whether a node has gone down or if instead there is network segregation: a serial port connection, common ping nodes (such as a router)...
I suspect that if reliable 2 node operation were designed into RBD, it would eventually replace some of the uses of DRBD.
2) Is there any way of preventing two users of an RBD device from using the device concurrently? Is there someway to create "locks" with RADOS that would die if a node dies? If so, this would allow an RBD device to be safely mounted as a non distributed FS such as ext3 exclusively on one of many hosts. This would open up the use of RBD devices for linux containers or linux vservers which could run on any machine in a cluster (similar to the idea of using it with kvm/qemu).
Thanks, I look forward to playing with RBD and ceph!
-Martin
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