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1clue
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PostPosted: Sun Aug 08, 2010 11:18 pm    Post subject: Xen, RAID, LVM2 and Gentoo. N00b questions. Reply with quote

Hi.

I'm looking into Xen. I'm working through the WIKI but some things are missing, and some things just are just not clear:


  1. I'm currently running Gentoo on RAID + LVM2. Can I slip Xen underneath that or do I need to reformat and recreate my partitions?
  2. Should I start over anyway even if I can slip the installation underneath the existing OS?
  3. Does Xen know about RAID and LVM2? Or is that the dom0 OS handling disk access?
  4. What is important in dom0?

    1. Do I just want a minimal distro with drivers and admin software, or can this be my main system?
    2. Do I want the inherent stability of staged releases, or the flexibility of a rolling release?

  5. Who lives in dom0? Is this a good place to work or is it like running Linux as root all the time?
  6. I've got an Asus P6T motherboard. Am I crippled until the proper bios comes out or does the setting to work around bad BIOS features fix it for VT-d?


Nothing I've seen really lets me know what is going to happen in dom0. My first inclination is that it should be an extremely minimal system and have nothing in it but the basics. As well, some sort of super stable heavily tested distro seems appropriate, and that I should not be very active in this VM except for updates and such.

The other end of the spectrum, maybe since the hardware access is unrestricted this might be where I want to live. I would suspect that hardware access would be much faster here.

Another thing that is freaking me out is disk partitions:

  1. I have 4 identical disks, organized as RAID. The /boot is a 4-way RAID 1 partition. Most of everything else is RAID 1 but only on 2 disks for each MD. There is also a RAID5 that I haven't actually installed anything on yet. I have 2 volume groups for LVM, each on its own MD pair. Mostly I have code in one and data in the other.
  2. Does Xen recognize this or is it irrelevant?
  3. Does partition optimization for a specific task go out the window, or how does one handle that? Do I put disk files on a partition of the appropriate type, and the app should take advantage, or do I put the disk files on an XFS filesystem and then format it internally to be the proper type, or can I assign real logical volumes to the appropriate VM?


I keep getting distracted in the documentation. I don't know if that's because the docs are organized poorly or if it's because I get sidetracked easily. Probably the latter. I'm bouncing all over the place on this, and not getting anything helpful out of the docs.

Thanks.
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PostPosted: Sun Aug 08, 2010 11:41 pm    Post subject: Reply with quote

I can't help you with XEN as I've never used it but if you do not want to change your setup much, and want to keep a usable main system, why not just use KVM?

Pretty much all you have to do for KVM, is create a LVM volume for it to use as storage, and it just works...
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PostPosted: Mon Aug 09, 2010 12:20 am    Post subject: Reply with quote

I also need to install a Windows 2003 developer image. I've looked through the most likely options and chose Xen. I already have experience with VMware and want to try something else.

Thanks.
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PostPosted: Tue Aug 10, 2010 4:43 pm    Post subject: Reply with quote

Quote:
1. I have 4 identical disks, organized as RAID. The /boot is a 4-way RAID 1 partition. Most of everything else is RAID 1 but only on 2 disks for each MD. There is also a RAID5 that I haven't actually installed anything on yet. I have 2 volume groups for LVM, each on its own MD pair. Mostly I have code in one and data in the other.
Does Xen recognize this or is it irrelevant?


It is irrelevant

Quote:
1. I'm currently running Gentoo on RAID + LVM2. Can I slip Xen underneath that or do I need to reformat and recreate my partitions?


Just emerge xen-sources and install the xen userspace tools. Leave the rest of your gentoo install alone.

Quote:
Who lives in dom0? Is this a good place to work or is it like running Linux as root all the time?

When I used xen, I used this as a normal machine.

Quote:
Nothing I've seen really lets me know what is going to happen in dom0. My first inclination is that it should be an extremely minimal system and have nothing in it but the basics. As well, some sort of super stable heavily tested distro seems appropriate, and that I should not be very active in this VM except for updates and such.


The reason is this decision is up to the user. The minimal approach is what vmware ESXi does. When I used xen I did not do that because I wanted at least part of the system that could run at 100% (disk and video) performance. An example of this is my dom0 had access to a RAID that did 300MB/s reads and writes while the domU guests maxed out at 150MB/s on the same RAID.
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1clue
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PostPosted: Tue Aug 10, 2010 6:18 pm    Post subject: Reply with quote

John,

Can you give an example of video performance on dom0/domU as well? Were you using VT-d?

I've signed up on the xen-users mailing list and got some of the same answers there, but not the performance issue with domU.

Most of my installs would not need huge performance, they just need to be available. I definitely want one Gentoo to be fast though.

Other than that I have started to solidify toward the minimal approach for dom0. But if there's that much of a disk hit I may change my mind.

Thanks.
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PostPosted: Tue Aug 10, 2010 6:23 pm    Post subject: Reply with quote

With xen I was using AMDs virtulization. For the video you can not do fully accelerated 3D in domU guest (no 3D games) without possibly allocating the GPU directly to the guest (never tried that) while obviously on the Dom0 you can make full use of your GPU and the rest of your hardware.


I do use kvm now for my i7 but no accelerated 2D / 3D in windows guests. It is however more reliable than vmware server and definitely more reliable than virtualbox.
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PostPosted: Tue Aug 10, 2010 7:11 pm    Post subject: Reply with quote

John,

I won't be doing anything fancy in Windows. That box is entirely populated with developer licenses, and using it for anything personal would be a violation of terms of use. I'm fussy about that. Besides, I really can't stand that OS. Wouldn't have it on anything of mine if I didn't have a really good reason.

As far as games on Linux, I haven't played any for at least 5 years, not counting an occasional minesweeper. I can see being interested in a flight simulator like X-plane, but haven't yet done anything about it. My main interest at this point would be video, as in movies. I have a video capture card and all, but one of the monitors has a TV tuner in it so I can go straight to that if it gets too problematic. I'm not doing anything tricky, just sometimes watch a movie on the monitor if the other TV is busy. My monitor is far better quality than the TV even if it is smaller.

I'm on the xen mailing list now, so I can get more details about speed and all from there.

I wonder if kvm and xen can be used simultaneously?

Never mind, I need to get my head wrapped around Xen first, that seems to be more useful to me at the moment.

Thanks again for your help.
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PostPosted: Tue Aug 10, 2010 7:37 pm    Post subject: Reply with quote

drescherjm wrote:
It is ... and definitely more reliable than virtualbox.
What kind of stability issues you ran into with virtualbox. I have used it to boot Windows XP, Linux, Solaris and never had issues. Just wondering...
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PostPosted: Tue Aug 10, 2010 7:45 pm    Post subject: Reply with quote

I am having serious problems with guest SMP and issues running on an i7 host both with 64 windows guests. Mostly X64 but I had issues with win7 x64 as well. The guests lockup and I also am having weird application issues. Messages like can not allocate enough storage space... The same exact guest container runs fine under kvm.
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PostPosted: Tue Aug 10, 2010 7:54 pm    Post subject: Reply with quote

drescherjm wrote:
I am having serious problems with guest SMP and issues running on an i7 host both with 64 windows guests. Mostly X64 but I had issues with win7 x64 as well. The guests lockup and I also am having weird application issues. Messages like can not allocate enough storage space... The same exact guest container runs fine under kvm.
So, if you disable SMP i.e. give only one CPU to the guest, the issues go away?
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PostPosted: Tue Aug 10, 2010 7:55 pm    Post subject: Reply with quote

Not on the i7 box but on the core2 quad.
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PostPosted: Tue Aug 10, 2010 8:04 pm    Post subject: Reply with quote

drescherjm wrote:
Not on the i7 box but on the core2 quad.
You mean on i7 box, if you give only 1 CPU to the guest, it still locks up but if you do that on core2 quad box, it doesn't lock up?
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PostPosted: Tue Aug 10, 2010 8:07 pm    Post subject: Reply with quote

I believe the lockup issue goes away on either but on the i7 box I still get application problems with SMP turned off and this is using the same exact guest that works under kvm with 4 guest cores.
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PostPosted: Tue Aug 10, 2010 8:13 pm    Post subject: Reply with quote

drescherjm wrote:
I believe the lockup issue goes away on either but on the i7 box I still get application problems with SMP turned off and this is using the same exact guest that works under kvm with 4 guest cores.
What do you use for graphical access in the guest with KVM? Does it have drivers for Windows/Solaris?
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PostPosted: Tue Aug 10, 2010 8:21 pm    Post subject: Reply with quote

I am not sure what windows driver I am using. I do know that I do not get accelerated 2D or 3D under windows. I can look at that later.

I think we are getting off the original topic. Should we start a new thread?
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PostPosted: Tue Aug 10, 2010 8:45 pm    Post subject: Reply with quote

drescherjm wrote:
I am not sure what windows driver I am using. I do know that I do not get accelerated 2D or 3D under windows. I can look at that later.

I think we are getting off the original topic. Should we start a new thread?
Yes, I think we are going OT. But the data point that vSMP is broken in VB is useful.

Can you please start another thread about KVM and video handling? I don't really want 2D/3D. I just want a mouse that move freely between guest and host.
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PostPosted: Sat Aug 14, 2010 3:02 am    Post subject: Reply with quote

BTW. I seemed to be able to fix my virtualbox SMP issue on i7 by reinstalling the guest.

Edit: To not clog this thread with my own discussion I am starting a different thread here: https://forums.gentoo.org/viewtopic-t-840066-start-0-postdays-0-postorder-asc-highlight-.html

to discuss optimization of 64 bit windows guests under gentoo virtulization.
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