Jun 192011

As I’ve been written on my previous post about Maildir Replication using ChironFS in postfix, I will explain step by step it can also be done by using drbd and ocfs2.

Compiling & Installing

note: if your Linux distribution is shipped with a kernel older than 2.6.33 you have to install a kernel module package and packages for the user land code. If your distribution contains a Linux-2.6.33 kernel or newer you only need to install the user land code.

In my case i have my linux distribution older than 2.6.33, so i will also compile drbd kernel module.

Download drbd source and create Binary RPMS packages

$ wget http://oss.linbit.com/drbd/8.3/drbd-8.3.10.tar.gz
$ tar xvzf drbd-8.3.10.tar.gz
$ cd drbd-8.3.10
$ ./configure --enable-spec --with-km
$ cp ../drbd*.tar.gz `rpm -E %_sourcedir`
$ rpmbuild -bb drbd.spec
$ rpmbuild -bb drbd-km.spec
$ sudo rpm -ivh /path/to/RPMS/drbd-*

I’ll be using loop files for this setup since I don’t have access to raw partitions. but if you have raw block device available you can subtitute this part:

resource r0 {
	meta-disk internal;
	device /dev/drbd0;
	disk /dev/loop0;


resource r0 {
	meta-disk internal;
	device /dev/drbd0;
	disk /dev/sdxx;

sdxx can be sda1, sdb1 sdb2 or what ever your raw disk device called

# dd if=/dev/zero of=/drbd-postfix.img bs=1M count=5000
# losetup /dev/loop0 /drbd-postfix.img

Place this DRBD resource file in /etc/drbd.d/r0.res. Be sure to adjust the server names and IP addresses for your servers.

resource r0 {
	meta-disk internal;
	device /dev/drbd0;
	disk /dev/loop0;

	syncer { rate 1000M; }
        net {
                after-sb-0pri discard-zero-changes;
                after-sb-1pri discard-secondary;
                after-sb-2pri disconnect;
	startup { become-primary-on both; }

	on postfix1 { address; }
	on postfix2 { address; }

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Jun 142011

When I was looking for ways to replicate the contents of memcached for high-availability performance, I found this memcached-repcached application. that has the ability to replicate the contents of one memcached to another.

Repcached key features

  • Multi master replication.
  • Asynchronous data repliacation.
  • Support all memcached command (set, add, delete, incr/decr, flush_all, cas)

People probably already know about memcached . It’s a robust, high performance key-value based memory object cache interface. but unfortunately, lack the ability to create redundancy and replication in memcached server clusters. although replication could be done at the application level. However, it all depends on each individual’s taste.

This is a quick and dirty experiment I have tried using memcached-repcached application on 2 servers.

Download memcached-repcached from repcached.lab.klab.org
Or you can download source rpm version from here

On the first server and second server extract memcached-1.2.8-repcached-2.2.tar.gz, compile with –enable-replication option when configure.

$ tar xvzf memcached-1.2.8-repcached-2.2.tar.gz
$ cd memcached-1.2.8-repcached-2.2
$ ./configure --enable-replication
$ make

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