I have been reticent to take this off the "zero-reply" list as I haven't touched this. However, I see no-one else has responded, so ...
This sounds like a "timing" issue.
Are you sure you don't have things arse-about ?. Maybe the DRBD [cs]hould be defined on LVM pv's, and contain a "simple" filesystem rather than (yet another) block device driver that LVM exposes. Redhat does the scan for LVM entities early in the boot process - if your network infrastructure isn't up and active, you won't find that LVM on DRBD.
nfs has a separate mount module that incorporates timeouts for fstab to ensure the network (eventually) comes up so mounts can complete. You might be in need of something similar.
Else you could remove the entries from fstab altogether and do the mounts in rc.local - also enables you to include sleep(s) in need.
Last edited by syg00; 09-05-2011 at 08:38 AM.