+MARS = Multiversion Asynchronous Replication System

+ +

MARS Logo

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GPLed software AS IS, sponsored by 1&1 Internet AG (www.1und1.de). Contact: tst@1und1.de

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+What is MARS Light?

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Main features:

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Anytime Consistency
Arbitrary Distances
Tolerates Flaky Networks

MARS Light is almost a drop-in replacement for DRBD (block-level storage replication). It runs as a Linux kernel module.

+ +

In contrast to plain DRBD, it works asynchronously and over +arbitrary distances. Our internal 1&1 testing runs between datacenters +in the US and Europe. MARS uses very different technology under the +hood, similar to transaction logging of database systems.

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Reliability: application and replication are completely decoupled. +Networking problems (e.g. packet loss, bottlenecks) have no +impact onto your application at the primary side.

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Anytime Consistency: on a secondary node, its version of the underlying +disk device is always consistent in itself, but may be outdated +(represent a former state from the primary side). Thanks to +incremental replication of the transaction logfiles, usually the +lag-behind will be only a few seconds, or parts of a second.

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Synchronous or near-synchronous operating modes are planned for +the future, but are expected to reliably work only over short +distances (less than 50km), due to fundamental properties +of distributed systems.

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WARNING! Current stage is BETA. Don't put productive data on it!

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+Documentation / Manual

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See https://github.com/schoebel/mars/blob/master/docu/mars-manual.pdf

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+Concepts

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For a very short intro, see my LCA2013 presentation docu/MARS_LCA2013.pdf .

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There is also an internal 2-years old concept paper which is so much outdated, +that I don't want to publish it.

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The fundamental construction principle of the planned MARS Full +is called Instance Oriented Programming (IOP) and is described in +the following paper:

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http://athomux.net/papers/paper_inst2.pdf

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+History

+ +

As you can see in the git log, it evolved from a very experimental +concept study, starting in the Summer of 2010. +At this time, I was working on it in my spare time.

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In Summer 2011, an "official" internal 1&1 project started, which aimed +to deliver a proof of concept.

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In February 2012, a pilot system was rolled out to an internal statistics +server, which collects statistics data from thousands of other servers, +and thus produces a very heavy random-access write load, formerly +replicated with DRBD (which led to performance problems due to massive +randomness). After switching to MARS, the performance was provably +better. +That server was selected because potential loss of statistics data +would be not be that critical as with other productive data, but +nevertheless it operates on productive data and loads.

+ +

After curing some small infancy problems, that server runs until today +without problems. It was upgraded to newer versions of MARS several +times (indicated by some of the git tags). Our sysadmins switched the +primary side a few times, without informing me, so I could +sleep better at night without knowing what they did ;)

+ +

In Summer 2012, the next "official" internal 1&1 project started. Its goal +was to reach enterprise grade, and therefore to rollout MARS Light on +~15 productive servers, starting with less critical systems like ones +for test webspaces etc.

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In December 2012 (shortly before Christmas), I got the official permission +from our CTO Henning Kettler to publish MARS under GPL on github.

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Many thanks to him!

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Before that point, I was bound to my working contract which kept internal +software as secret by default (when there was no explicit permission).

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Now there is a chance to build up an opensource +community for MARS, partially outside of 1&1.

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Please contribute! I will be open.

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I also try to respect the guidelines from Linus, but probably this +will need more work. I am already planning to invest some time into +community revision of the sourcecode, but there is not yet any schedule.

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In May 2013, I got help by my new collegue Frank Liepold. He is working +on a fully automatic test suite which automates regression tests +(goal: rolling releases). That test suite is based on the internal +test suite of blkreplay and can be found in the test_suite/ subdirectory.

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In November 2013, internal 1&1 projects started for mass rollout to several thousands of servers.

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Although the software continues to be labelled "beta" for the next future, it has reached enterprise grade due to our internal rating process.

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+Future Plans

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Smaller Reworks: in Winter 2013/2014, some smaller changes to the symlink tree are planned, in order to make it more readable for humans and to prepare for future enhancements. They will only change the syntax, not the semantics. There will be an uprade plan, i.e. the old symlink tree remains usable; only newly created clusters will use the new structure.

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In parallel, the software will be internally divided into three parts:

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Generic brick framework
AIO personality with XIO bricks
MARS Light application

I hope this will make MARS more attractive for the mainline Linux kernel community.

Mars

Asynchronous Block-Level Storage Replication