Re: Replacing DRBD use with RBD

[Alex Elsayed <eternaleye@gmail.com>]

Martin Fick wrote:

> Hello,
> 
> I have a questions with respect to RADOS and RBD and the cluster monitor
> daemons.

I'm not one of the developers, but I've been following for a while and one 
of your sub-questions intriqued me; specifically:

>...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).

As it currently stands you could likely run a vserver or an 
OpenVZ/Virtuozzo/LXC container on Ceph (the distributed FS) directly, rather 
than layering a local FS over RBD. Also, this would probably provide better 
performance in the end. As a side benefit, you would gain the ability to 
make fine-grained snapshots of the guests' filesystems, access them directly 
from the host (or another Ceph client), and adjust quotas for the guest 
while running. This is probably a better solution for container-based 
virtualization than RBD-based options, due to the advantage one can take of 
all guests sharing a kernel with the host. RBD is more likely to be useful 
for full virtualization like KVM, but even in that case you could probably 
make a specialized initramfs that mounts a rootfs over Ceph with a prefix 
(taking advantage of that Ceph allows mounting a subdirectory as if it was 
the whole FS).

Hope this helps!