I did that yesterday and wanna provide help to anybody else trying.
If you try, some of the following issues should be expected:
- Grub2 can’t handle the /boot volumes that worked with grub. It tries to embed itself right behind the partition start and somehow can’t, although grub is doing just fine…
- Grub2 will at times not be able to grub-update
- You’ll have to manually install the new xen kernels & utils (thats fixable)
- Xen “Default Utils Path” handling will break until you installed all xen pieces (a debian cludge) (thats fixable)
- If you created a /usr/bin/pygrub symlink to work around idiocy, adjust it for xen 4 (thats fixable)
- You’ll not have nic firmware even though you have non-free in your apt sources.list. (firmware-realtek is the package you need) (thats fixable)
- Grub2 is per default misconfigured and will not boot into Xen. See the order of stuff in /etc/grub.d, you have to take care that your xen kernel (20_linux_xen) is called before the standard linux kernel (10_linux). Doesn’t that rock? over 30kB of Grub2 config scripts and in the end you have to rename files to work around logic failures.
- Setting GRUB_CMDLINE_XEN=”noapic” in /etc/default/grub takes no effect.
- Hetzners vKVM really rocks, but you can’t avoid noticing that KVM is still a piece of crap, so Xen can’t boot up in it due to buggy hardware emulation (apic bugs), which means you can’t look into Xen boot issues.
- Unless you’re a real genious you might wanna hardcode a non-automagic boot entry in grub.conf and default to that. (heavily recommended)
- If you start/stop xendomains and it uses xm save to supsend the VMs, a few times, debian lenny VMs might hang due to clock backstep issues. (fixable: turn off suspend)
- I couldn’t find a trace of tmem, might that be due to the pv_ops dom0 kernel? Does it not have any *features*? (not fixable unless you wanna use non-distro kernel)
- xm new (proper way of creating vm’s) is broken.
- if you get an incomprehensibly stupid error upon xm create of a HVM domU, install the qemu drivers (xen-qemu-dm-4.0) (thats fixable)
Needless to say most of these issues already had accompanying bug reports, some dating back to 2008, most include details on solving the issue that are being ignored.
The curious mind might also enjoy googling for grub2 disaster or grub2 nightmare, the number of results is pretty impressive for a software this young.
Myself, I’ll ditch this host for one using Oracle VM quite soon using koan –replace-self. The 1% performance gain over a pvops kernel is just a cherry on top.
Please look at my newer Post ‘squeeze + xen” – the Debian Wiki now has info on a larger number of the issues I encountered.