Firstly let me state that the "problem" exist for elder releases probaly as well.

For xen you can define partitions for DOMu in two ways: either as a file or as a raw partition. For several reasons i choosed to use a file.
Traditionally i split major file systems in seperate partitions for "normal" unix installations. So I did this also with XEN.

I noticed that for each file-image that is fed to the DOMu, a loopback device is used. If one uses eight partitions for a DOMu, all is fine. But beyond that DOMu wont start and even worse is does not give a clue why not.

After some expermenting i found that the number of loopback devices is by default set to eight. Which implies that one can create either one DOMu with 8 partitions, or eight domains with one partition.
Or increase the number of loopback devices.

As it is nolonger a module, on has to set it as a kernel parameter in the grub-config (max_loop=256) and create the devices in /dev.

Specially when using a XEN-kernel, it would be nice if the number of loopback devices were already increased to 256.

As XEN is going to be included into sles-10, it would be a nice enhancement, small as it is. Specially as XEN does not come with a clear error (neither from xm, neither in /var/log/xend.log)

Hans