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Re: [Xen-devel] [RFC Patch 00/25] COarse-grain LOck-stepping Virtual Machines for Non-stop Service

At 2014/7/18 22:18, Andrew Cooper Wrote:
On 18/07/14 12:38, Wen Congyang wrote:
Virtual machine (VM) replication is a well known technique for providing
application-agnostic software-implemented hardware fault tolerance -
"non-stop service". Currently, remus provides this function, but it buffers
all output packets, and the latency is unacceptable.

In xen summit 2012, We introduce a new VM replication solution: colo
(COarse-grain LOck-stepping virtual machine). The presentation is in
the following URL:

Here is the summary of the solution:
>From the client's point of view, as long as the client observes identical
responses from the primary and secondary VMs, according to the service
semantics, then the secondary vm is a valid replica of the primary
vm, and can successfully take over when a hardware failure of the
primary vm is detected.

This patchset is RFC, and implements the frame of colo:
1. Both primary vm and secondary vm are running
2. do checkoint

This patchset is based on remus-v15, and use migration v1. Only supports hvm
guest now.

TODO list:
1. rebase to remus-v17 or newer
2. support migration v2
3. nic/disk replication
4. support pvm

This is an interesting set of patches.  One query I have is what you
mean by "support migration v2".

While I am developing migration v2, the old legacy code is left in place
for easier testing and development purposes, but when the migration v2
code does finally get committed, the legacy migration code will be

The legacy code is unfit for purpose and entirely replaced by v2, in a
backwards-compatible manor given the included conversion script (not
that that matters for Remus/colo).

We use migration to implement remus/colo. If migration v2 is merged into upstream
xen, I think I need to add codes to migration v2, and make colo can work
with migration v2.

Wen Congyang


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