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
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