[sheepdog-users] Live migration of VM disk from one sheepdog node to another

[Struan Bartlett]

Hi

I am experimenting with different options for distributed storage of 
KVM/QEMU virtual machine disk images. I like the simplicity of setup of 
sheepdog+corosync, and the homogeneous nature of this installation (each 
server is the same). However, given our current distribution of raw 
metal servers, I'm not sure it makes sense to us that every VM host 
should be running sheepdog. This is because the raw metal servers we 
have with the greatest RAM and spare processing capacity, also have the 
strongest disk storage which is heavily utilised. Conversely, we have 
other raw metal servers that are shorter on RAM and spare CPU capacity, 
but have plenty of free disk space. Our VMs are used for development and 
testing purposes, and don't need to be high powered. It therefore seems 
to make sense to run sheepdog on the machines with plenty of free disk 
space, and the VMs on the machines with plenty of CPU and RAM.

I know this is possible with sheepdog, since the qemu driver supports 
talking to sheepdog on a remote host, and I've managed to get that 
working. What I don't know is, whether there are any plans to make it 
possible to migrate VMs backed by such storage from one sheepdog node to 
another. This is important for when a sheepdog server needs to be taken 
down for maintenance. For example, is it planned to either (a) allow the 
choice of remote sheepdog server backing the guest disk to be changed 
on-the-fly? (b) Allow a set of remote sheepdog servers to be specified 
for the guest disk, allowing the qemu driver to automatically failover 
from one to another in the event the sheepdog node becomes inaccessible? 
or (c) use a protocol such as rbd (like Ceph) that supports talking to 
multiple storage servers natively?

Kind regards

Struan

-- 

Struan Bartlett
NewsNow Publishing Limited

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