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[Xen-users] Looking for suggestions with multiple issues

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Subject: [Xen-users] Looking for suggestions with multiple issues
From: James Pifer <jep@xxxxxxxxxxxxxxxx>
Date: Tue, 20 Oct 2009 14:52:54 -0400
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I've been tossing the idea around of switching to XenServer. I have
XenServer installed on a machine and the management features look pretty
cool. The downside is that I would need to convert 30+ domU's and I'm
really not sure I want to do that. I've played around and haven't
converted one successfully yet. I also haven't made any progress in
connecting to ocfs2. 

My current environment runs great except for a few things. I currently
have 3 xen servers sharing an ocfs2 cluster and it works great. I'm
running xen 3.2.x on sles10sp2. The performance is great for my running
domU's, but here are the things that frustrate me though: 

1) The biggest issue is with memory. At some point xen seems to lose the
ability to manage free memory, no matter how much you have reporting as
free. This has been discussed recently on the list. This is apparently
directly related to how many times you stop/start/restart domUs. Just
recently one of my servers had 10+ gb of free ram, but I couldn't add or
restart any domU's. To fix the problem I had to restart dom0, obviously
not something you want to do if you have important systems running. 

This is a huge issue for me. I'm thinking about testing the latest
stable release from source and see if anything has improved. So far I've
only installed what Novell has released through their updates. The other
problem is this issue can take a long time to present itself, so it's
something that's not easy to test.

I feel it's unrealistic to try and limit your reboots. You can to a
degree, but some things just require it. 

2) I'm not sure what the proper way to handle the auto starting domains.
Also talked about on the list recently (search for "config.sxp pain -
auto start?"). In the old 3.0 days is was a simple softlink
in /etc/xen/auto to the config in /etc/xen/vm, at least on sles. Since
3.2 I've tried using the xenstore, but this is such a pain. To create a
new domU it takes these steps:
1) I create a new domU with virt-manager
2) I then shutdown the domU 
3) save a conf of the domU: xm list -l  [domU name] > [domU name].conf
4) edit this conf file for the start and stop lines
5) remove the domU from virt-manager
6) reinstall it with: xm new -F [domU name].conf

This is creating, stopping, and starting a domU, see problem #1! This
process has also not always worked. Sometimes I find the start line
still not updated in xenstore. 

3) I have not figured out a good way to give people access to a domU.
Right now I use vnc, but this is assuming the domU is installed. I have
not figured out how to give someone the ability to run there own
install, although it seems possible through vnc somehow. Also going back
to #1, people are able to restart their domUs. That's not a function we
want to take away, but it contributes to #1. 

4) Attaching cdroms has been a problem. Thankfully it doesn't come up
very often, but there are times I need or want to be able to access a
cdrom from a domU. I really haven't gotten this to work at all.   

Let me be clear, I think xen is great. I would appreciate any thoughts
or suggestions on these issues.


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