[DRBD-user] Do You Always Have to Upgrade/Rebuild DRBD Whenever You Upgrade the Kernel?

[Roland Kammerer]

On Fri, Apr 22, 2022 at 09:05:46PM +0000, Eric Robinson wrote:
> Thanks for the feedback, Roland. I am actually a paying Linbit
> customer, but I am unaware of the process to follow when upgrading the
> OS. For example, I'm currently running Rocky Linux 8.5 (kernel
> 4.18.0-348.2.1.el8_5.x86_64) and drbd 9.19.1-1.el8.

The name of the meta package (i.e., "drbd") is IMO pretty unfortunate,
that version refers to DRBD utils. It does not matter, can not remember
when we did a breaking change in utils. What matters is kmod-drbd. But
you most likely know that.

> There is a kernel
> upgrade to 4.18.0-348.20.1.el8_5 available in the Rocky repo. If I
> install that, does it break drbd?

In 99.9% it does not break the binary module. That would only be the
case if the vendor broke the kAbi. We usually have 1 binary module per
RHEL dot release. So as long as you don't jump from like RHEL 8.4 to 8.5
or something then the same module should be fine. Also, you might enable
a "dot repository" (one that has .../rhel8.5/... in the URL, not the
global ".../rhel8/..." one that contains all the kernel modules for all
RHEL (8.0, 8.1, 8.2,...) if you are a customer. If you enabled the "dot
repo" you should be fine taking the latest kernel + the latest
kmod-drbd. If, and that is very unlikely, there are more than 1
kmod-drbd in a dot repo, use the one closest to your kernel version,
usually the later one. Again, that usually is not the case, only if the
kAbi was broken.

Finding the best matching kernel module to a given kernel for all DRBD
modules that exist is a problem we had to solve ourselves, we even have
a public web service one can use like this:
$ cat /etc/os-release | curl -T - -X POST drbd.io:3030/api/v1/best/$(uname -r) -s

At the time of writing it answered with:
kmod-drbd-9.1.7_4.18.0_348-1.x86_64.rpm

If you are into RHEL versioning, you see that this is the first
kernel-devel package in that kernel series. So, for 4.18 there has not
been any breakage. Which again is the usual case, the people at Redhat
know what they are doing. Most of the time :).

Code for that web service and the underlying python library can be found
here:
https://github.com/LINBIT/bestdrbdmodule
https://github.com/LINBIT/python-lbdist

Regards, rck