upgrading my dom0 box (again?) - foolish?

[Jeff Rizzo <riz%tastylime.net@localhost>]

Greetings, all-

It's been... maybe almost a decade?  Since I was actively paying regular 
attention to the goings-on in the world of Xen under NetBSD, and I find 
myself with a dom0 host which I've been thinking I would retire for... 
maybe 5 years now?  :)  I've come to the realization, though, that I'm 
at least a full year (realistically... more) away from retiring this 
machine, which means it's in desperate need of an upgrade, if only so I 
can actively use it until I retire it.


So... I'd like to politely request a little guidance from folks more 
up-to-date than I am.  I'm reading the port-xen pages at wiki.n.o, and 
this mailing list.  I've done a Xen upgrade on this host before, but 
that was from (I think?) 4.8 to 4.11, and I have only very vague 
memories of what what involved.   I *am* aware that much progress has 
been made in recent years with various virtualization methods - and one 
of the ideas prodding me to upgrade now (instead of continuing to 
ignore) is maybe installing a new domU or two with the "latest" 
virtualization - but I don't want to add any more legacy stuff. :-P


Anyway, from what I can tell, here's what this host is:

- core i5 with (I think) 16GB of physical RAM (could be 8GB or even 4- 
the domUs and dom0 are only using 3.5GB total), running a Xen 4.11 
hypervisor with NetBSD 9.2/amd64 dom0

- a pair of 2TB drives in a raidframe mirror for storage.  domUs are 
using LVMs diced up out of /dev/raid1e

- 5 active domUs.

- One of the important ones is an i386 PAE domU.  It's... possible to 
migrate the stuff on there to something less ancient, but I'd much 
rather do so *after* an upgrade if I can help it (perhaps I can't, which 
wouldn't be the worst thing in the world).  I believe this one is fully 
PV (I load the domU kernel from the dom0 file system), and it's running 
NetBSD 8.1/i386

- the other 4 domUs are running NetBSD/amd64, various versions of 
NetBSD/amd64 with XEN3_DOMU kernels (one 6.0_RC2 (!), the rest 
9.0_STABLE).  These load the kernel with pygrub - which I understand to 
be fully deprecated at this point, and I no longer even recall how I set 
it up :). Also, that 6.0_RC2 domU can likely just be shut down at this 
point.

- all of the domUs have a single "disk" which is an LVM logical volume 
of either 5 or 10GB.

- the Xen tools and such were installed with pkgin from pkgsrc; probably 
binaries from ftp.n.o.  These are the Xen packages currently installed:

xenkernel411-4.11.4nb6 Xen 4.11.x Kernel
xenkernel413-4.13.3  Xen 4.13.x Kernel
xenkernel48-4.8.3    Xen 4.8.x Kernel
xentools411-4.11.4nb5 Userland Tools for Xen 4.11.x


... I vaguely recall having a problem with Xen 4.13 at the time, which 
is why 4.11 is what's running.


So.  Is there any hope for moving this to Xen 4.20 and a NetBSD 10.1 
dom0, or should I just leave well enough alone and phase this system out 
entirely?  (I certainly want to do that in the long run, but it feels 
like it could give me another couple years)

If I were to do an upgrade, can someone suggest a good order of 
operations with fallback?  Apologies for the vagueness of this - but 
clearly I've been out of Xen world for a while now.  :)

Thanks in advance,

+j