ES master: srv101:

yum install mysql-server

add these lines to /etc/my.cnf [mysqld] section:

log-bin
server-id=1002101
skip-name-resolve
key_buffer_size=100M

Run:

# chkconfig mysqld on
# service mysqld start

Write down:
# mysql -e 'show master status'
+-------------------+----------+--------------+------------------+
| File              | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+-------------------+----------+--------------+------------------+
| srv101-bin.000003 |     4155 |              |                  |
+-------------------+----------+--------------+------------------+

# mysql < ~midom/php/maintenance/ourusers.sql
# mysql -e "GRANT REPLICATION SLAVE ON *.* TO repl@10.0.2.101 IDENTIFIED BY '$(<repl-password)'"
# mysql -e "GRANT REPLICATION SLAVE ON *.* TO repl@10.0.2.102 IDENTIFIED BY '$(<repl-password)'"
# mysql -e "GRANT REPLICATION SLAVE ON *.* TO repl@10.0.2.103 IDENTIFIED BY '$(<repl-password)'"

ES slave: srv102

yum install mysql-server
add these lines to /etc/my.cnf [mysqld] section (only ID differs):

log-bin
server-id=1002102
skip-name-resolve
key_buffer_size=100M

# chkconfig mysqld on
# service mysqld start
# mysql -e "CHANGE MASTER TO MASTER_HOST='srv101',MASTER_USER='repl',MASTER_PASSWORD='$(<repl-password)',MASTER_LOG_FILE='srv101-bin.000003', MASTER_LOG_POS=4155 "

Same on srv103, just change the ID.

Then on zwinger:

# cd ~/midom/php/maintenance/storage
# ./make-all-blobs srv101

In case of properly running replication, this command on zwinger should work:

# sql -h srv103 -e 'show create table blobs \G' enwiki
*************************** 1. row ***************************
       Table: blobs
Create Table: CREATE TABLE `blobs` (
  `blob_id` int(10) unsigned NOT NULL auto_increment,
  `blob_text` longblob,
  PRIMARY KEY  (`blob_id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 MAX_ROWS=1000000 AVG_ROW_LENGTH=1000000


Add these lines to db.php:
'cluster17' => array(
        '10.0.2.101' => 1,
        '10.0.2.102' => 1,
        '10.0.2.103' => 1,
),

Add or replace old cluster in:
$wgDefaultExternalStore = array( 'DB://cluster17');