Some applications require direct access to a block device, without an intermediate file system. Some Oracle and MySQL configurations are an example, as are some Xen setups, or IET. Can you do this with DRBD? Sure you can.

However, you need to fulfill two prerequisites:

1. Your application can’t access DRBD while it’s in the Secondary role. So, you must make sure DRBD is Primary before your application attempts using that device.
2. The user in whose context your application runs needs read/write access to that device.

Your cluster manager, when configured properly, normally takes care of item #1 for you. #2 is a little trickier:
Normally, DRBD’s device nodes are owned by root:disk, with permission bits set to 0660 (rw-rw----). So in order to allow your application to use the device, you have two options:

• Add …

A question I recently got from our friends at MySQL:

When speaking about DRBD, we mention that if you upgrade your Linux kernel, it is important that you also upgrade the version of DRBD appropriately.
Question: When upgrading the kernel via yum/yast, does it automatically detect that you should also upgrade your DRBD module?

The answer is, as always, a clear and resounding “it depends.”
Let’s break this down by distribution.

• If you’re on Debian and updating your linux-image package, dpkg will complain about an unresolved dependency from the DRBD kernel module package, forcing you to update that as well.
• If you’re on Debian and adding a more recent linux-image package, it’s up to you to remember to install a new DRBD kernel module package as well.
• If you’re on …