[Sheepdog] Backup/Images

[Yibin Shen]

we have talked about similar topic in the past weeks.

IMO, let sheepdog support local backup image will promote the availability effectively,
the local backup image is located in the machine where vm runs,
then writeback policy is adopted just like what qcow/qcow2's backup image do.

the storage size issue can be solved through decrease the number of copies.

benefits:
1)network traffic will be reduced, which will also make corosync work more stable.
2)even whole sheepdog cluster crashed, the local image can still provide service.

tradeoffs:
1)stronge consistency is damaged for I/O is not triggered synchronously now.
  to solve this problem, at least we need maintain a journal for local backup image.
2)migration of vm will became much more complicated.

so, maybe this is only a transitionary solution before sheepdog archive industry available standard.


Yibin Shen
On Sat, Oct 8, 2011 at 3:28 AM, Mark Pace <pace at jolokianetworks.com<mailto:pace at jolokianetworks.com>> wrote:

On 10/7/2011 1:20 AM, MORITA Kazutaka wrote:


- hide quoted text -

Other than the storage size issue, the backup node would be a
bottleneck if there are many VMs. The backup node requires a huge
amount of disk space and bandwidth, but if we could use such machine,
we wouldn't need a clustered storage system. However, on a small
cluster environment with a few nodes, the backup node idea looks good.
If someone sends a patch to support it, I'll accept it.  Thanks,
Kazutaka


I'm not sure I agree.  Shared storage is a single point of failure and
the reason we're looking to Sheepdog is the ability to survive a shared
storage outage.  Pumping a shared storage box up to provide a backup
location is not nearly as expensive as creating a redundant/replicated
shared storage environment that is capable of serving virtual machines
properly.  But, that being said, your absolutely correct in that machine
is going to be beefy in large environments, etc.

Now, I'm not a programmer, but would happily pay for someone to write it
-- if anyone is interested, please contact me.


Mark Pace


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