[buug] Xen sational!(?)

Michael Paoli Michael.Paoli at cal.berkeley.edu
Wed Apr 8 03:51:15 PDT 2009

Quoting "Ian Zimmerman" <itz at buug.org>:

> I now have two periods of renting a xen virtual server behind me, and I
> am firmly convinced that, for that purpose, it sucks.  In a nutshell,
> the problem is that while you have root on the guest system, you can't
> reconfigure or upgrade the kernel.
> Now, if you have control over the hypervisor, and use virtualization
> to isolate apps from one another, that may be a very different story.

Well, I've got a mixed impression of Xen ... lots of stuff going for it,
but on the downside:
o documentation's still pretty sucky last I checked in detail, anyway.
   OpenSource is good - but it's no substitute for good documentation
   (e.g.  one shouldn't have to grok Python to be able to determine how
   to get a Xen guest to boot off of an alternate (real or virtual)
o paravirtualization - more efficient (saves space and all that), but
   it's not full virtualization, and it does quite intertwine guest and
   host kernel
o full virtualization - on hardware that supports it ... I haven't had
   opportunity to try that yet with Xen ... but that would have it's
   advantages (and also disadvantages)

As far as a hosting provider (e.g. renting a Xen guest) - with full
virtualization, it should be feasible to allow guests to update their
kernels (and to allow reconfigurations of the guests) ... that doesn't
necessarily mean it's easy to provide that service or there's anyone out
there doing it yet.  With paravirtualization, guest kernel is very
tightly bound to host kernel ... so changes there will likely be rather
to quite restricted.

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