Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 03/09/2011 09:18 AM, Felix Frank wrote: >>> while partitioning a partition is possible and rather straight-forward, >>> it sure isn't standard practice. >> >> I wasn't actually suggesting to create "partitions in partitions" I just >> wasn't aware that the drbd device nodes are partitions and not basic >> block devices (like i.e. the /dev/xvdN nodes that xen adds). That >> certainly explains the behavior I'm seeing. > > You're right, technically DRBDs are not harddrive partitions (I think). > This had me wondering: What is your backing device? I was assuming you > created a DRBD on top of a physical partition. All of this is happening in a xen VM an I use a dedicated virtio disk as backing device i.e. in this particular case it is /dev/xvdc for drbd resource r1 (/dev/drbd1). /dev/xvda is the system disk and /dev/xvdb is the backing device for drbd resource r0 (/dev/drbd0). r0 is already setup as redundant nfs share using pacemaker which works nicely. What I am now trying to do is to also make iSCSI LUNs highly available next to the nfs share. >>> Also, please make sure that replication actually works when you mount >>> your "inner partitions" this way. I think it should, but I might be >>> wrong. >> >> I'm sure one could make this work but I don't intend to try it. I've >> seen people use logical LVM volumes as physical volumes for new volume >> groups which *seemed* to work though I didn't know for sure because I >> was too busy trying to get out of there. Always fun to see these kinds >> of M.C.Escher-esque topologies....as long as I don't have to maintain >> them :) > > Within the DRBD paradigm, this is actually a common and documented > approach: http://www.drbd.org/users-guide/s-nested-lvm.html Yes, though I'm keen to avoid going too deep with kind of nesting because of my experiences. In the case I mentioned the guy managed to create loops where a volume nested inside a logical volume was added as a physical volume for the volume group of it's parent. The results weren't pretty. So eventually I will probably end up using LVM maybe even in a nested fashion but for now I try to keep things simple for the sake of making experimenting/debugging easier. > What I'm saying is: You *are* mounting nested partitions using kpartx. > I'd be interested in whether this is supported and works wrt. replication. So far I've used kpartx mostly to mount partitions inside the lvm backing device for a virtual machine on the host. If I were to use this in this case that would probably require a modification of the pacemaker ocf scripts so that kpartx gets called automatically when the state of the drbd device changes. That sounds rather fiddly and non-robust so I will just skip this experimental step and go straight to the lvm on top of drbd step. Regards, Dennis