The ELRepo Project has DRBD packages for CentOS-5 and CentOS-6, named drbd83-utils or drbd84-utils. The CentOS Project does not want to maintain extra packages that exist in other places unless we need to change them ... so we are not going to create DRBD packages for CentOS-6.
Since CentOS-4 is being EOL'ed in less than a month, we are also not going to publish updates for the DRBD in CentOS-4.
This leaves the DRBD for CentOS-5 that are part of CentOS Extras. Since these have been released for CentOS-5, we will continue to maintain the DRBD version 8.3.x tree (drbd83) in CentOS Extras.
A new version of DRBD 8.3 (drbd83-8.3.12) has been released to the testing repository for CentOS-5. You can see the details here:
DRBD 8.3.12 for CentOS-5
If you want to use DRBD 8.4.x for CentOS-5, rather than releasing it separately, the CentOS Project recommends that you use drbd84-utils from ELRepo (linked above).
For users who want to use the drbd83-8.3.12 version ... please test the version that is currently in CentOS Testing and provide feedback. With enough feedback I will move the packages from testing to CentOS Extras.
NOTE: These packages have now been moved to CentOS Extras and can be installed normally with yum.