drbd-8.2.4 as P/P setup (storage fun, part 2)

NOTE: Now on www.mass-storage.org, this blog-post isn’t up-to-date anymore. Please see mass-storage.org for the up-to-date labs note.

Fun stuff with DRBD

Ok, so yesterday, I’ve tried without much success to rebuild my computer lab with Debian/SID and unstable DRBD-8.2.5. Now that I know that the main branch of drbd can contain "unusable version", it will go a bit faster.

Installation of DRBD-8.2.4 took around 60 seconds, most of it being the download from their website and the copy of the source tree between Crystal and Ruby, my two lab systems.

# cd /usr/local/src
# wget http://oss.linbit.com/drbd/8.2/drbd-8.2.4.tar.gz
# tar xvf drbd-8.2.4.tar.gz
# apt-get install linux-headers-`uname -r` build-essential flex docbook-utils
# cd /usr/local/src/drbd-8.2.4
# make all
# make install

Online verification of the sync. status

Now the fun part :

(ruby)# drbdadm verify store

It worked like a charm. I used the "verify-alg md5;" line in my config since the kernel crypto. API already had this algorithm available and loaded. Being able to have an online verify allow me to remove the "data-integrity-alg" function I had in some of my setup – verification once a while does really reduce the cpu processing overhead of DRBD. 

The crypto. API interface speed can be tested with

# openssl speed

and currently available (loaded) functions can be queried with :

# cat /proc/crypto

Adding some security

Another thing I had never tried in the past is activating this security feature :

(/etc/drbd.conf)# cram-hmac-alg "md5" ;
(/etc/drbd.conf)# shared-secret "password";

Once again, worked as supposed. I can now see the HMAC handshake when the peer connect. The module is automatically loaded in the crypto API.

Primary/Primary setup ?

Now, here is the true test I wanted to do.

(/etc/drbd.conf)# uncommenting the "allow-two-primaries" line
(ruby&crystal)# /etc/init.d/drbd stop ; /etc/init.d/drbd start
(ruby&crystal)# drbdadm store primary

I now have a Primary/Primary setup. Fun, yet we need a filesystem with support for concurrent connections. Lets go for OCFS2 (The docs say that GFS is also supported).

(ruby&crystal)# apt-get install ocfs2-tools
(ruby&crystal)# mkdir /etc/ocfs2

The creation of the config file is very straight forward :

(/etc/ocfs2/cluster.conf)

node:
ip_port = 7777
ip_address = 10.0.0.18
number = 0
name = crystal
cluster =lab

node:
ip_port = 7777
ip_address = 10.0.0.19
number = 1
name = ruby
cluster = lab

cluster:
node_count = 2
name = lab

Configuration of the Heartbeat process is also very easy (careful to use the good cluster name).

(ruby&crystal): dpkg-reconfigure ocfs2-tools

Then the magic begin:

(ruby&crystal)# /etc/init.d/o2cb start
(ruby)# mkfs.ocfs2 /dev/drbd0
(ruby&crystal)# mount -t ocfs2 /dev/drbd0 /storage

Et Voila.

Concurrent access to the same filesystem on 2 computers. Some-one said "Cheap load-balancing/hot-fail-over for web-server" ? For the optimization part, can I loudly suggest to go, at the very minimum, with giga speed network interfaced… which bring the point that infiniband isn’t the price it used to be… and performance/latency are really a big step forward…

220-602 is very easy if you already have 640-863 and 642-432 or only 70-297 on your credit. However, going for EX0-100 might be a bit more difficult and doing 70-431 would help tremendously.