Tracy R Reed wrote:
We are commenting on the use of the phrase "minimal hypervisor". The
hypervisor is different from the userland. Who cares how big the
userland is? You don't need special block drivers for xen. I can point
xen at my iso or /dev/cdrom just fine without involving any special
block device drivers.
Only because you're in Linux accessing to a Linux, so the call passes
through. The block driver basically doesn't have to do much translation
so is easy to write. Xen relies on the fact that it has a compatible
DomU that can handle a lot of the translation in order to minimize the
amount of translation in the hypervisor itself.
This is the reason why Xen has been such a PITA for most of the stuff
I've been trying.
Try it on OpenSolaris Dom0 for an eye-opener. You can't install from a
CDROM because the block drivers don't exist that will allow access to
the CDROM (thus the loopback NFS mount workaround). This is because you
can't just "pass through" a device API call from a DomU to a Dom0 like
you can from Linux-to-Linux.
And, before you go blaming OpenSolaris too much, this is an x86 machine
so it has the standard BIOS, etc. that could be used for basic install
work. But, of course, Xen's real-mode emulation is broken so that
doesn't work either. Oops.
And why do you think the xen guys are obligated to code for your favored
OS? Why don't the people who are interested in your OS write the code?
Surely they would be much better at it.
They're not under any such obligation. However, if they choose that
path, then they don't get to claim to be a real virtualization solution.
Nor do they get to claim to be "open source" when you need their $1000
drivers to make Windows work.
You don't get to claim all the buzzwords and then not deliver and not
get slagged for it.
I'm wondering if, perhaps, we aren't looking at Xen through different
perspectives. I note that you tend to use the 3.0 Xen series. Is that
before or after they got bought? You may be looking at Xen through
rose-colored glasses before their corporatization and expecting too
little, while I may be looking at Xen through black-colored glasses
after the marketechture hype moved in (and having previously used
VMWare) and expecting far too much.
I am *not* a happy puppy with Xen. It's been a long time since I have
been quite this unhappy about an OS implementation/feature. The last
time was probably when I finally had enough of crappy Linux video
drivers and changed to OS X. I expect open source OS breakage; it goes
with the territory. I've even written my own device drivers when
required. However, this one has really ticked me off. I haven't quite
figured out why.
I think it's probably the fact that I feel a lack of quality. I'm about
to trust my server to a bunch of folks who can't keep something working
that they had working a version ago? The FreeBSD guys didn't bother
trying to be a DomU because the API was in such flux that it wasn't
worth their time. Is that something I really am going to trust? The
folks writing Xen have pulled their Windows drivers closed-source. Am I
comfortable with a company that is clearly prioritizing Windows users to
that extent? How do I know that Xen won't pull the same stunt as VMWare
and make their extra driver management Windows-only?
I also think that Xen got pulled into the production before it was ready
because the company is trying to prevent VMWare from getting an
entrenched position. Thus, I'm reacting to the fact that Xen is too
technically premature to be garnering the marketing push that it is
getting. I probably shouldn't have looked at it yet.
Xen is fine for Linux in Linux (but only for certain favored flavors).
Nothing else.
Having actually run a lot of stuff under xen I have to disagree.
That is your opinion, and it was your opinion and a couple of others
that made me even consider trying Xen in advance of what I normally
would. Normally, I wait until I hear about a technology from one of my
bellwhethers before trying it out. I violated that rule for Xen.
At this point, I *might* recommend it for Linux-on-Linux. Maybe. If
Windows is on the menu, I would steer them at VMWare.
Otherwise, I'd tell them to talk to one of the companies that stuffs 2
or 4 small machines in a 1U case and look at Xen in a couple of years.
It might be a real product by then.
Good software takes 10 years. Xen probably needs 3 more years yet.
-a
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