CentOS 5.3 64bit, XEN and DRBD

Well, seeing as though I pulled my hair out solving this, let me answer my question and save someone else the trouble of hair pulling :)

Solution:

After playing around, plenty of Googling and repartitioning etc... I came to a setup that works like a charm.

There is probably a quicker way to do this but I am not going to over complicate this answer

I did a standard install with the partitions like this (I have a 500g hard drive) :

/boot 100mb 
/swap 4gb 
/     40gb 

The balance of the disk space is to be left as unpartitioned space.

Then, I created a primary partition called /dev/sda4 by following these steps:

~: fdisk /dev/sda
~: (fdisk shell) p4   (for primary partition # 4)
~: (fdisk shell) t    (hit t and enter to edit the partition type)
~: (fdisk shell) 08e  (Linux LVM)

Reboot the server so that the new partitions can take effect.

Now create logical volumes by:

~: pvcreate /dev/sda4
~: vgcreate xenvg -s 4M /dev/sda4    # (xenvg is the name of my virtual group, you can rename it)
~: lvcreate -L400G -n xenroot xenvg  # (xenroot is going to be my drbd  resource and root partition for my DomU)
~: lvcreate -L4G  -n xenswap xenvg   # (xenswap is my swap file for my DomU)

Now that you have the correct partitioning you can go ahead and install DRBD with the following config file directives (drbd.conf)

Just displaying the 2 important directives here...

{
device  /dev/drbd0;
disk    /dev/xenvg/xenroot;
}

Your XEN VM config file needs to look like this (again, just the important one)

{
disk = [ "drbd:xenvm,xvda,w","phy:xenvg/xenswap,xvdb,w" ]
}

I hope this helps someone out there...

No, I've never seen the issue. But it sounds messy. This may be a hosting support issue. If the host pushes a specific kernel version and they manage the R1Soft install, shouldn't the host have a working hcp module available or be able to walk users through the steps needed to get things working? If anything, you can try hcp-setup and upload the relevant info to R1Soft's build servers. I've never had to build the module locally, but I'm usually on distro kernels or slightly-modified distro kernels.