Export your block devices with AoE

Posted by rodo on Thu 11 Oct 2007 at 08:59

Imagine you have a machine with all of his disk full and another with unused Gigabits, and you don't want to move the data from one to other. Why not using the second's disk on the first, you can do it with iSCSI but you can do it with ATA over Ethernet (AoE) too. It's the second method I'll explain is this article.

All of this was made with two computer running Debian Etch.

Prepare the kernel

First check if your running kernel have AoE, the config option name is CONFIG_AT_OVER_ETH, have a look at fig1, my kernel has AoE in module

fig1

host:/# grep ATA_OVER /boot/config-`uname -r`
CONFIG_ATA_OVER_ETH=m
host:/#

If not, configure your kernel and activate AoE in core or in module like you prefer

Device Drivers -->
  |- Block Devices --->
      |-  <m> ATA over Ethernet support

Ok now you have a kernel with AoE, just load the aoe module

host:/# modprobe aoe
host:/#

You can check your syslog to be sure AoE is available

host:/# tail /var/log/syslog
Oct 10 11:54:07 host kernel: aoe: aoe_init: AoE v22 initialised.
host:/#

Now we'll call the client 'client' and the server 'server', funny isn't it ?
In SAN vocabulary we call the client 'initiator' and the server 'target', I prefer to continue using simplest therms.

The server side (target)

In first we need to install the vblade package

server:/# apt-get install vblade
Reading package lists... Done
Building dependency tree... Done
The following NEW packages will be installed:
  vblade
[...]
Unpacking vblade (from .../archives/vblade_11-1_i386.deb) ...
Setting up vblade (11-1) ...
server:/#

On our server we'll export the /dev/sdd5 partition which has a size of 5GB, export a block device is easy at do

server:/# vbladed 0 1 eth0 /dev/sdd5
server:/#

Some explication about this command, each AoE device is identify by a couple Major/Minor, with major between 0-65535 and minor between 0-255. AoE is based just over Ethernet on the OSI models so we need to indicate which ethercard we'll use.
Is this example we export /dev/sdd5 with a major value of 0 and minor if 1 on the eth0 interface.
We are ready to use our partition on the network !

Client Side (initiator)

The client needs the aoe kernel module too, so prepare your kernel as we saw.
The userlands tools are present in the package aoetools

client:/# apt-get install aoetools

Now discover what we can use over our network :

client:/# aoe-discover
client:/# aoe-stat
      e0.1         5.000GB   eth0 up
client:/#

At this point we have a new block device available on the client box named /dev/etherd/e0.1. If we have a look at the /dev tree a new node appears

client:/# ls -al /dev/etherd/
total 4
drwxr-xr-x  2 root root     140 2007-10-10 13:30 .
drwxr-xr-x 16 root root   14660 2007-10-10 13:30 ..
c-w--w----  1 root disk 152,  3 2007-10-10 13:30 discover
brw-rw----  1 root disk 152, 16 2007-10-10 13:30 e0.1
cr--r-----  1 root disk 152,  2 2007-10-10 13:30 err
c-w--w----  1 root disk 152,  4 2007-10-10 13:30 interfaces
-rw-r--r--  1 root root       5 2007-10-10 13:00 revalidate

What to do with

Simply make a filesystem on your block device like

client:/# mkfs.ext3 /dev/etherd/e0.1

and use it like you do with your /dev/hd* or /dev/sd* the only difference is that block device is over the network !

This article can be found online at the Debian Administration website at the following bookmarkable URL:

http://www.debian-administration.org/articles/553