Re: [gentoo-user] Xen vs Citrix XenServer

[Felix Kuperjans]

On 2012-01-01 18:40, Tanstaafl wrote:
> Thanks for your response Michael...
>
> On 2012-01-01 11:51 AM, Michael Mol <mikemol@×××××.com> wrote:
>> On Sun, Jan 1, 2012 at 11:18 AM, Tanstaafl wrote:
>> While I haven't played with XenServer, I have played with its
>> open-source clone, XCP, and was very annoyed by it. I'd rather run a
>> Gentoo dom0.
>
> I just thought that running a bare metal hyperviser would be more
> stable/reliable, and running it on a thumb drive would be much more
> convenient.
With Xen (or XenServer) the hypervisor always runs on bare metal, and
the domain-0 and its kernel is a special kind of a virtual machine (it
has virtual RAM and virtual CPUs as any other Xen domain, but
additionally full hardware access especially to all PCI devices and ACPI
/ sensors etc.). Separating it on a thumb drive will not change a lot,
the hypervisor gets loaded into RAM any way and does not require any
disk access. However, the domain-0 operating system will usually use a
disk (but could also be run by NFS root file system or anything else).
>
>>> First - I want to use a bare metal hypervisor that supports the
>>> following:
>>>
>>> 1. Can be installed on a USB FLASH drive (I have some Dell
>>> Poweredge 2970 servers with the internal USB slot for just this
>>> purpose), and
>
>> I don't think I've heard of anyone doing this, but I don't see why
>> it'd be a problem.
>
> Definitely not a problem for XenServer (although v6 isn't officially
> supported on a thumb drive yet), so I was mainly wondering about Xen
> itself...
>
>>> 2. Fully supports both Windows Server 2008 (our Domain Controller),
>>> and Gentoo Linux (our mail and web servers).
>
>> The xen supports hvm, where it emulates hardware; in a full hvm VM,
>> *any* operating system comfortable on x86 should run.
>>
>> There's also paravirtualization, which is faster, and is likely what
>> you're thinking of wrt 'bare metal'. Signed drivers for paravirt
>> mode for hardware (such as your network, disk or system clock) are
>> available for current versions of Windows.
>
> Yes, PV is what I was thinking of, thanks - and apparently this
> wouldn't be a problem with gentoo either?
I'm using a Gentoo domain-0 and domU systems productive for more than 2
years now. I have never used a virtual machine with Windows Server
running, but it's fully supported by both, open-source Xen and XenServer.
>
>>> I can't seem to find an ebuild for the xenserver tools, and when
>>> looking found out about Xen (I had thought that it went away a long
>>> time ago)...
>
>> * app-emulation/xen-tools
>>       Available versions:  3.4.2-r3 ~3.4.2-r5 ~4.1.1-r5 4.1.1-r6
>> ~4.1.2-r2!t {acm api custom-cflags debug doc flask hvm pygrub qemu
>> screen xend}
>>       Homepage:            http://xen.org/
>>       Description:         Xend daemon and tools
>
> Hmm... so will these tools work with XenServer? Or are they just for Xen?
>
> Also, I ran across an article on the gentoo wiki that said that the VM
> images for Xen and XenServer are NOT compatible, which I find odd if
> XenServer is just Xen with some additional tools provided by Citrix.
>
> The article also said that the single biggest advantage of XenServer
> is the amount of time required to get something up and running -
> minutes for XenServer, compared to days for Xen - is this dated info,
> or still true?
I don't know about the setup of XenServer, but it should be rather
straightforward. XCP is also meant to be a quick way to setup Xen just
as VMWare ESXi or something similar. Setting up Xen in a Gentoo domain-0
is much more work for sure, but (as always with Gentoo) gives you lots
of possibilities for customization.
>
>> * sec-policy/selinux-xen
>>       Available versions:  [M]2.20110726
>>       Homepage:
>> http://www.gentoo.org/proj/en/hardened/selinux/
>>       Description:         SELinux policy for xen
>>
>> * sys-kernel/xen-sources
>>       Available versions:
>>          (2.6.18-r12)    2.6.18-r12!b!s
>>          (2.6.34-r3)     ~2.6.34-r3!b!s
>>          (2.6.34-r4)     ~2.6.34-r4!b!s
>>          (2.6.38)        ~2.6.38!b!s
>>          {build deblob symlink}
>>       Homepage:            http://xen.org/
>>       Description:         Full sources for a dom0/domU Linux kernel to
>> run under Xen
>
> I though that xen-sources were no longer needed as of kernel 2.6.33+?
2.6.37+, but the first *really* usable kernel is 3.1, because earlier
ones didn't have blockback support (virtual disks), up to 3.0, and 3.0
had a serious bug with VGA output. In addition, there may be performance
problems with those kernels in some applications (but I didn't
experience any yet).
>
> Thanks again Michael,
>
> Charles
>
>
Regards,
Felix