COLO FT/HA (COarse-grain LOck-stepping Virtual Machines for Non-stop Service)
project is a high availability solution. Both primary VM (PVM) and secondary VM
(SVM) run in parallel. They receive the same request from client, and generate
response in parallel too. If the response packets from PVM and SVM are
identical, they are released immediately. Otherwise, a VM checkpoint (on demand)
is conducted.

See the website at https://wiki.xen.org/wiki/COLO_-_Coarse_Grain_Lock_Stepping
for details.

Remus provides fault tolerance for virtual machines by sending continuous
checkpoints to a backup, which will activate if the target VM fails.

See the website at https://wiki.xen.org/wiki/Remus for details.

Using Remus with libxl on Xen 4.5 and higher:
 To enable network buffering, you need libnl 3.2.8
 or higher along with the development headers and command line utilities.
 If your distro does not have the appropriate libnl3 version, you can find
 the latest source tarball of libnl3 at http://www.carisma.slowglass.com/~tgr/libnl/

Disk replication:
 VMs protected by Remus need to use DRBD based disk backends. Specifically, you
 need a compile and install a custom version of DRBD, that is available publicly
 at https://github.com/rshriram/remus-drbd
 This code is based on DRBD 8.3.11 and uses a new replication protocol (named
 protocol D) for asynchronous disk checkpoint replication. A protected VM's DRBD
 disks on the primary and backup hosts need to be configured to use protocol D
 as the replication protocol. An example resource configuration file can be found
 in the aforementioned github repository.

Sphinx documentation:

All source rendered by Sphinx is licensed under CC-BY-4.0.

You are free to:
  Share:
    Copy and redistribute the material in any medium or format.
  Adapt:
    Remix, transform, and build upon the material for any purpose, even
    commercially.

Under the following terms:
  Attribution:
    You must give appropriate credit, provide a link to the license, and
    indicate if changes were made. You may do so in any reasonable manner, but
    not in any way that suggests the licensor endorses you or your use.
  No additional restrictions:
    You may not apply legal terms or technological measures that legally
    restrict others from doing anything the license permits.

See https://creativecommons.org/licenses/by/4.0/ for full details.

This includes:
  * All ReStructured Text files:          docs/*/*.rst
  * The Sphinx configuration file:        docs/conf.py
  * Content in Sphinx-exclusive subdirs:  docs/*-guide/*


Other documentation:

There are a variety of text documents in various formats.  These, given no
explicit license guidance, fall under Xen's default GPL-2.0 license.

Last Index update Sat Jun 03 09:59:21 CST 2023