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        "pages": {
            "263": {
                "pageid": 263,
                "ns": 0,
                "title": "Remus",
                "revisions": [
                    {
                        "contentformat": "text/x-wiki",
                        "contentmodel": "wikitext",
                        "*": "<!-- The page has been confirmed to be up-to-date for Xen 4.5 -->\n__NOTOC__\n\nRemus provides transparent high availability to ordinary virtual machines running on Xen. It does this by continually live migrating a copy of a running VM to a backup server, which automatically activates if the primary server fails. Key features:\n\n* The backup VM is an exact copy of the primary VM (disk/memory/network). When failure occurs, the VM continues running on the backup host as if failure had never occurred.\n* The backup is completely up-to-date: even active TCP sessions are maintained without interruption.\n* Protection is transparent: existing guests can be protected without modifying them in any way.\n\n= Host (dom0) requirements =\n* Xen hypervisor with remus support and tools (included with Xen 4.0+)\n** Note: Remus is not included with XCP, XenServer, or with some of the Linux pre-packaged versions of Xen, so please check your distribution or you may need to build Xen from source\n* Xen dom0 kernel that meets the [[Remus dom0 requirements]]\n* Shared storage is not required\n* DRBD shared storage is supported, allowing faster and automatic re synchronization after a failed host is brought back online\n** Otherwise to bring a failed node back online, the VM must be turned off to perform disk re-synchronization\n\n= Guest (domU) requirements =\n* Xen PV guests that meet the [[Remus PV domU requirements]]\n* Xen HVM guests don't require any changes for Remus\n\n= Installation =\nInstallation varies slightly depending upon the host platform, so please see the guides below for examples.\n\n* [[Install Xen 4.5 with Remus and DRBD on Ubuntu 12.10]]\n* [[Install Xen 4.2.1 with Remus and DRBD on Ubuntu 12.10]]\n* [[Install Xen 4.1.4 with Remus and DRBD on Ubuntu 12.10]]\n\n= DRBD support =\n\nUsing DRBD instead of blktap2 for storage replication allows for quick re-synchronization of the disk backend after failed host is back online. Since storage (re)synchronization is done online - while the VM is operational, there is no need to shutdown the VM. Once storage is synchronized, one can start, stop and restart Remus on a running VM anytime.\n\nHowever, DRBD must be custom built with support for protocol D (see the above install guides), so the normal packaged versions of DRBD are not suitable.\n\nNote that DRBD will be operated in dual primary mode, which carries a number of risks and management issues. Please research this topic to be aware of the potential complications.\n\n* [http://remusha.wikidot.com/#toc4 Install DRBD 8.3.11 (remus version) on Debian Squeeze/Ubuntu 10.04] \n* [[Install Xen_4.2.1 with Remus and DRBD on Ubuntu 12.10#Install_DRBD| Install DRBD 8.3.11 (remus version) on Ubuntu 12.10]]\n\n= Limitations =\n* For PV domUs, Remus requires \"suspend event channel\" kernel support. This support has not yet been upstreamed to the Linux kernel [[XenParavirtOps#Upstream_delta_details|at the time of the Xen 4.5 release]]. Otherwise Remus can run most any PV domU in a degraded performance mode. This kernel support is not widely available (not currently available in Ubuntu, for example), but is available with OpenSUSE. See [[Remus PV domU requirements]] for more information.\n\n= Release History =\n\n== Xen 4.5 ==\n* Significant improvements to Remus in Xen have been contributed, such as better [[XL]] integration, better DRDB support, stability and performance improvements and enablement of COLO support\n* See [[Remus_Toolkit_Differences#Xen_4.5_and_newer|Remus command line syntax in Xen 4.5]]\n* COLO support [although COLO itself is not currently expected to be fully available until 4.7] (see [http://www.xenproject.org/help/presentations-and-videos/video/xpds13v-colo-update.html COLO XPDS13 video], [http://www.xenproject.org/help/presentations-and-videos/video/xpds13-colo.html COLO XPDS13 presentation])\n\n== Xen 4.4 ==\n* Experimental support for xenlight (xl). Per the man page, there is no support for network or disk buffering at the moment.\n\n== Xen 4.2 ==\n* Many bugfixes to Remus.\n* Remus support for pvops domU kernels: Linux 2.6.39.2 and later upstream kernel.org versions are now supported as PV domU kernels, in addition to Jeremy's xen.git xen/stable-2.6.32.x branch.\n* For better Remus performance you should use a domU kernel with \"suspend event channel\" support, which means linux-2.6.18-xen, or any of the xenlinux forwardports (novell sles11sp1 2.6.32 kernel, for example). pvops domU kernels don't have suspend event channel support yet.\n* Checkpoint compression for less data to transfer between hosts.\n\n== Xen 4.0.1 ==\n* Pvops dom0 kernel support for Remus has been added in Xen 4.0.1-rc4, so it's available in Xen 4.0.1 final release. You can use Linux 2.6.32 based pvops dom0 kernel with Remus.\n* PV domU kernel still needs to be linux-2.6.18-xen.\n\n== Xen 4.0.0 ==\n* Xen hypervisor and tools have Remus support.\n* Only linux-2.6.18-xen is supported as Xen dom0 kernel with Remus.\n* If using a PV domU you need to run linux-2.6.18-xen as domU kernel.\n\n= Links =\n* The \"xl remus\" command has a similar, but not identical, syntax to the traditional Xend based \"remus\" command.  See [[Remus_Toolkit_Differences]].  Also, \"xl remus\" still has limitations in the 4.4 release, per the man page.\n* Research papers about Remus:\n** [http://http://www.cs.ubc.ca/~andy/papers/remus-nsdi-final.pdf Remus - NSDI 2008] Design and fundamental concepts.\n** [http://http://www.cs.ubc.ca/~andy/papers/secondsite-vee-final.pdf SecondSite - VEE 2012] Remus in wide-area, with checkpoint compression, replication and storage re-synchronization using DRBD. \n* Configuring and installing Remus (Xend version) with DRBD, Xen 4.1.2 under Debian Squeeze/Ubuntu 10.04: http://remusha.wikidot.com/\n* Video demonstration of Remus: http://joburg.eu/en/video/2jV4lOgFJMY/Screen-cast-Remus-High-Availability-based-on-Xen-Hypervisor\n* Source code for Remus version of DRBD 8.3.11 http://remusha.wikidot.com/local--files/configuring-and-installing-remus/drbd-8.3.11-remus.tar.gz\n\n[[Category:Xen]]\n[[Category:Xen 4.5]]\n[[Category:Users]]\n[[Category:Developers]]\n[[Category:Project]]\n[[Category:HowTo]]\n[[Category:Glossary]]\n[[Category:High Availability]]"
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            "1580": {
                "pageid": 1580,
                "ns": 0,
                "title": "Remus PV domU requirements",
                "revisions": [
                    {
                        "contentformat": "text/x-wiki",
                        "contentmodel": "wikitext",
                        "*": "Remus supports most domU guests that can be run in PV, however, you may see this warning when you start Remus:\n<pre>\"WARNING: suspend event channel unavailable, falling back to slow xenstore signalling\"</pre>\n\nThis means the kernel in the guest doesn't have \"suspend event channel\" support, which in turn basically Remus is going to work, but isn't going to perform well. \n\n* At the time of the Xen 4.5 release, the [[XenParavirtOps#Upstream_delta_details|PVOPS kernel does not support this feature]]\n* At the time of writing, Ubuntu kernels do not generally have suspend event channel support\n* On the subject of adding support to a kernel's source, according to the author of Remus, \"It is not a config option. It requires some code modification and cannot be selectively enabled, in a clean way.\"\n* The [http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/ linux-2.6.18-xen.hg] kernel from Xen does have support, but is old these days and probably not a great choice\n* [http://www.opensuse.org/en/ OpenSUSE] natively supports suspend event channel support, and is a good choice for testing\n* Yes, this does mean that it's not necessarily easy to start using Remus for production with any given domU in PV\n* Note: You can instead run your VM in HVM without requiring this support, if that is an option for you\n\n= References =\n* xen-users thread about suspend event channel support: http://www.gossamer-threads.com/lists/xen/users/271981\n* See [http://www.gossamer-threads.com/lists/xen/devel/344236 remus suspend event channel in pvops kernel (Aug 2014)]\n\n[[Category:Xen]] [[Category:Compatibility]] [[Category:Users]] [[Category:High_Availability]]"
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