Oreilly Webcast 01 19 10

DRBD & MySQL An HA Match Made In Heaven

What is DRBD?
Distributed replicated block device
Sits between filesystem & hardware dev
Software-based mirroring

HA with MySQL Replication
Fast & easy setup
Statement based problems
Non-deterministic functions
Asynchronous - time lag
Requires monitoring error log
Maatkit mk-table-checksum

HA with MySQL & DRBD
Active/passive cluster
Exact copy of mysql db
Small performance hit using /dev/drbd0 versus /dev/sda1

Intro to Sun’s Virtualbox
Supports Mac, Windows, Linux
Simple installer
Build VMs easily
Add virtual external disks

Downloads
Virtualbox
virtualbox.org/wiki/Downloads
CentOS
wiki.centos.org/Download

Create Your VMs
Create vm using GUI
User Storage tab - Add 2nd disk - 25m scsi
Config networking interface
Bridged adaptor
Download CentOS DVD ISO image
Use storage tab - select ISO image
Start VM running - boot iso dvd
Install CentOS 5.4
Edit /etc/hosts file

Install DRBD on Both Nodes
$ yum install drbd
$ yum install kmod-drbd
$ yum install emacs

Configure DRBD
Edit drbd.conf
common { protocol C; }
resource sean {
on adelie {
device /dev/drbd0;
disk /dev/sda1;
meta-disk internal;
address 192.168.0.106:7789; }
on african {
device /dev/drbd0;
disk /dev/sda1;
meta-disk internal;
address 192.168.0.105:7789; } }

Protocol C?
C - write IO is reported as completed, if we know it has reached _both_ local & remote DISK
for critical transactional data.
B - write IO is reported as completed, if it has reached local DISK and remote buffer cache.
for most cases.
A - write IO is reported as completed, if it has reached local DISK and local tcp send buffer.
for high latency networks
benchmarks have shown that C is actually better than B.

What is meta-disk?
Drbd stores metadata
Internal - end of your volume
External - /dev/hda3…
Swapping hd is slightly different

Start DRBD
Be sure iptables is stopped
$ /etc/init.d/iptables stop
$ fdisk /dev/sda
$ drbdadm create-md sean
$ /etc/init.d/drbd start
$ drbdadm -- --overwrite-data-of-peer primary sean
$ watch cat /proc/drbd
$ mkfs.ext3 /dev/drbd0
$ mount /dev/drbd0 /mnt/mysql

Configure MySQL & Start
$ yum install mysql-server.x86_64
Edit /etc/my.cnf
datadir=/mnt/mysql
$ mysql_install_db
$ mysqld_safe &
Login & create test.demo_tbl

Test Switching Nodes
On adelie do:
Stop mysql
$ umount /mnt/mysql
On african do:
$ drbdadm primary sean
$ mount /dev/drbd0 /mnt/mysql
$ mysqld_safe &

Using Heartbeat
/etc/ha.d/ha.cf
/etc/ha.d/haresources
/etc/ha.d/authkeys
Stop mysql
umount /mnt/mysql
$ /etc/init.d/heartbeat start
/var/log/heartbeat-debug.log

The Whole HA Stack
drbd - mirror fs, software SAN
mysql - built on drbd volume
Heartbeat
Lvs
Virtual IP
Start, stop services
heartbeat

Conclusions
Alternative to MySQL Repl.
Requires some sysadmin skills
Combined with Heartbeat
Automatic failover
Virtual IP address for both servers

Further Reading
ProMySQL: Kruckenberg& Pipes
High Perf MySQL: Lentz, Zaitsev, Tkachenko, Sawodny, Balling, Schwartz
mysqlperformanceblog.com
planetmysql.com

About Us
Sean Hull
[email_address]
www.oracleopensource.com
www.linkedin.com/in/hullsean

Oreilly Webcast 01 19 10

by Sean Hull on Feb 05, 2010

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Oreilly Webcast 01 19 10 — Presentation Transcript

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