Installing DRBD On Hardy!

DRBD (Distributed Replicated Block Device) is a technology that is used to replicate data over TCP/IP. It is used to build HA Clusters and it can be seen as a RAID-1 implementation over the network.

As you may all know, the DRBD kernel module has now been included into Hardy Heron Server Edition’s kernel, so there is no more source downloading and compiling, which makes it easier to install and configure. Here I’ll show you how to install and and make a simple configuration of DRBD, using one resource (testing). I’ll not cover how to install and configure heartbeat for automatic failover (This will be showed in a next post).

First of all, we will have to install Ubuntu Hardy Heron Server Edition on to servers and manually edit the partition table. We do this to leave FREE SPACE that we will be used later on as the block device for DRBD. If you’ve seen the DRBD + NFS HowTo on HowToForge.com, creating the partitions for DRBD and leaving them unmounted will NOT work, and we won’t we able to create the resource for DRBD. This is why we leave the FREE SPACE, and we will create the partition later on, when the system is installed.

So, after the installation we will have to create the partition, or partitions (in case we are creating an external partition for the meta-data, but in this case it will be internal), that DRBD will use as a block device. For this we will use fdisk and do as follows:


fdisk /dev/sda
n (to create a new partition)
l83 (to create it as logical and format it as Filesystem # 83)
w (to write the changes)

After creating the partitions we will have to REBOOT both servers so that the kernel uses the new partition table. After reboot we have to install drbd8-utils on both servers:

sudo apt-get install drbd8-utils

Now that we have drbd8-utils installed, we can now configure /etc/drbd.conf, which we will configure a simple DRBD resource, as follows:

resource testing { # name of resources

protocol C;

on drbd1 { # first server hostname
device /dev/drbd0; # Name of DRBD device
disk /dev/sda7; # Partition to use, which was created using fdisk
address 172.16.0.130:7788; # IP addres and port number used by drbd
meta-disk internal; # where to store metadata meta-data
}

on drbd2 { # second server hostname
device /dev/drbd0;
disk /dev/sda7;
address 172.16.0.131:7788;
meta-disk internal;
}

disk {
on-io-error detach;
}

net {
max-buffers 2048;
ko-count 4;
}

syncer {
rate 10M;
al-extents 257;
}

startup {
wfc-timeout 0;
degr-wfc-timeout 120; # 2 minutos.
}
}

Note that we are using drbd1 and drbd2 as hostnames. This hostnames must be configured and the servers should be able to ping the other via those hostnames (that means we need to have a DNS server or configure hosts for both servers in /etc/hosts).

After creating the configuration in /etc/drbd.conf, we now can create the DRBD resources. For this we issue the following in both servers:

sudo drbdadm create-md testing

After issuing this, we will be asked for confirmation to create the meta-data in the block device.

Now we have to power off both servers. After powering them off, we start our first server and we will see something similar to this:

After confirming with ‘yes’, we can now start the second server. After the second server is running. both nodes resources are secondary, so we have to make one of them primary. For this, we issue the following on the server we would like to have the resource as primary:

drbdadm -- --overwrite-data-of-peer primary all

We verify this by issuing:

cat /proc/drbd

And this should show something like this:

Well, up to this point, i’ve have showed you how to install and configure DRBD on Hardy, and how to make one of the servers have its resource as primary. But, we still don’t have automatic failover or automatic mounting. In a next post I’ll show how to configure heartbeat to have automatic failover and to take control of the resources, aswell as configuring STONITH to use the meatware device, so that we won’t have a split-brain condition (or at least try). I’ll also show how to configure NFS and MySQL to use this DRBD resource.

BTW, if you have questions you know where to find me🙂.

17 Responses to “Installing DRBD On Hardy!”

  1. ryan Says:

    Just to be I am speaking from personal experience here, not as a hater or anything. However I just want to say that DRBD has some really significant drawbacks in real world scenarios.

    One sad part of life is that sometimes filesystems get corrupted — maybe bad hardware, some freak bug, whatever — the point is that when they do DRBD will happily replicate your corruption across the network. So at 3:00am when it breaks you have to inform your boss that your HA cluster is actually not so much HA after all. This might be OK for NFS if your data is easily recoverable from backup, but for a large database that is a very bad thing and painful to recover from.

    That said, your tutorial is good. Much simpler now that the kmodule is in Hardy!

  2. Ante Says:

    Why would you power servers down? Just start the drbd service. I would suggest using redhat-cluster-suite instead of HA. That gives you an option of using GFS on top of DRBD. And if you configure primary-primary DRBD with GFS, you could write on the same drbd disk at the same time from two different servers.

  3. Shang Says:

    Great article! But, how do we remove DRBD and rebuild it with another machine?

  4. jimcooncat Says:

    Thank you so much! I am installing DRBD this month, and it’s so timely you wrote about this. Looking forward to your next installment on Shoot The Other Node In The Head!

  5. roaksoax Says:

    Ante: I’m not fan of redhat-cluster-suite, but HA also gives the option to have DRBD in a primary/primary configuration, by installing a Cluster FileSystem such as GFS or OCFS. But it guess it is just a little bit harder to configure.

    Shang: the only thing you can remove is drbd8-utils package. Removing it won’t remove the kernel module, but it will remove all the DRBD config files and tools, and it would be as if there was nothing installed, because the DRBD’s kernel module won’t be used.

    ryan: Surely DRBD has its drawbacks as every piece of software. On the other hand, DRBD have options to deal with data corruption and so on… Btw, DRBD has paid support. Linbit.com is the company behind DRBD, and, if it wasn’t a good alternative instead of having a SAN, Linbit wouldn’t have as many clients as they do around europe and the US. But well, as you said… it is all about personal experiences.

  6. Installing DRBD on Hardy Part 2. « RoAkSoAx’s Weblog Says:

    […] DRBD on Hardy Part 2. As you know, in a previous post I showed how to install DRBD in Hardy Heron, in an active/passive configuration. Now, I’m […]

  7. Andres Rodriguez: Installing DRBD on Hardy Part 2. | Christian eBuddy Blog Says:

    […] you know, in a previous post I showed how to install DRBD in Hardy Heron, in an active/passive configuration. Now, I’m […]

  8. Zyga Says:

    Slightly offtopic.

    Could you please describe the machine that was running in the screenshots? I’m particularly interested in processor count.

  9. roaksoax Says:

    Well it is my Desktop:

    Processor: AMD Athlon 64 X2 3000+
    RAM: 2Gb Kingston (800Mhz)
    HDD: Samsung 250GB 7200 rpm
    MB: Asus M2N SLI
    Video: nVidia 8500GT

    I got running up to 6 VM’s simultaneously (2x64bit and 4x32bit Guests). Ubuntu Server, with 256 Ram each VM.

  10. Alex Says:

    I found your site on technorati and read a few of your other posts. Keep up the good work. I just added your RSS feed to my Google News Reader. Looking forward to reading more from you down the road!

  11. Derek Says:

    I disagree
    Can you give more info?

  12. roaksoax Says:

    More info about what?

  13. DRBD and NFS « RoAkSoAx’s Weblog Says:

    […] as you may know, in previous posts (Post 1, Post 2) I’ve showed you how to install and configure DRBD in an active/passive configuration […]

  14. BigFish Says:

    I’ve just recently started experimenting with DRBD and it is confusing! Your tutorial did help a little though. Thanks

  15. sandrar Says:

    Hi! I was surfing and found your blog post… nice! I love your blog. 🙂 Cheers! Sandra. R.

  16. Gonzalo Says:

    Thank you roaksoax. It was very helpfull.
    One simple question. How can I automate to send me an email when it fails?…thats it, if ever the primary fails, and the secondary takes the control.
    I do not mean the task of sending the mail with an MTA, which I know how to do it, but where can I put this script to send the mail or if there is any elegant way to do it. Thanks


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