[gentoo-user] Xen questions

[gentoo-user] Xen questions

[Xavier Parizet]

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Hi everyone,

I saw recently on some others threads that virtualization is being used by some
of you. So, i have a question : currently, i'm running a dedicated server under
Xen 3.3.1 and xen-sources-2.6.18-r12, with 11 domUs, all running Gentoo of
course, and on amd64. But, i was wondering about the used kernel version.

Indeed, these one begin to be very old, and i saw that on some other linux
distributions, the used kernel version is 2.6.25. So here are my questions :

  - why 2.6.21 stays masked on ~arch (last entry in changelog date of 31/08/2008) ?
  - is someone still working on Xen in Gentoo ?
  - i know about kvm, so is there any reason to migrate to KVM instead of Xen ?

Thanks a lot for your opinion.

Best regards.

-- 
      Xavier Parizet
YaGB :   http://gentooist.com
GPG  :    C7DC B10E FC21 63BE
B453 D239 F6E6 DF65 1569 91BF



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Re: [gentoo-user] Xen questions

[Heiko Wundram]

On Tue, 08 Sep 2009 16:38:16 +0200, Xavier Parizet <xav@gentooist.com>
wrote:
>   - why 2.6.21 stays masked on ~arch (last entry in changelog date of
>   31/08/2008) ?

2.6.21 was a forward-port done by some Gentoo-guys based on the
2.6.18-kernel that was part of Xen 3.1.3 (IIRC). It's _old_, really old,
that's why it's hardmasked. The current 2.6.18-based Xen-kernel ebuild is
the kernel (patch) that's included with Xen 3.3 (again, IIRC). There are no
newer _official_ Xen-kernels (at least none newer than 2.6.18), and the
Gentoo-developers decided not to include a forward-port anymore, as it
quickly becomes unmaintainable when the version difference between kernel
trunk and Xen kernel becomes larger.

There are forward-ports done by some other distributions (the 2.6.25 you're
hinting at is the Xen-kernel forward port of the Debian-guys, IIRC).
Someone is rebasing the SuSE-forward-ports of the Xen-kernels to Gentoo,
and is offering ebuilds for download here:

http://code.google.com/p/gentoo-xen-kernel/downloads/list

The kernels offered by the SuSE-developers are at most 1-2 minor revisions
behind the current vanilla kernel (as far as i can tell). I've been using
those rebased SuSE-Xen-kernels productively on a Gentoo machine since quite
some time, and they've always been very stable.

>   - is someone still working on Xen in Gentoo ?

Yes. To convince you, Xen 3.4.1 took about a day (post release by the Xen
developers) to be included in ~x86-portage.

>   - i know about kvm, so is there any reason to migrate to KVM instead of
>   Xen ?

If you're currently using HVM, partially; HVM is in portage (and is also
maintained), so you wouldn't need to rely on outside ebuilds, but the
respective infrastructure for maintaining HVM-based machines from the
command-line is poor (there's no such thing as xm and init-scripts, which
can be a major PITA). If you're using para-virtualized kernels, then
definitely no, as HVM fully virtualizes all I/O (which degrades disk-IO
considerably more than a paravirtualized Xen instance), unless you're
adventurous and willing to play with virtio-drivers, which I could never
get completely stable.

YMMV, and HTH!

-- 
Heiko Wundram
Gehrkens.IT GmbH

FON 0511-59027953 | http://www.gehrkens.it
FAX 0511-59027957 | http://www.xencon.net

Gehrkens.IT GmbH
Strasse der Nationen 5
30539 Hannover

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Geschäftsführer: Harald Gehrkens, Daniel Netzer

Re: [gentoo-user] Xen questions

[Xavier Parizet]

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Heiko Wundram a écrit :
> On Tue, 08 Sep 2009 16:38:16 +0200, Xavier Parizet <xav@gentooist.com>
> wrote:
>>   - why 2.6.21 stays masked on ~arch (last entry in changelog date of
>>   31/08/2008) ?
> 
> 2.6.21 was a forward-port done by some Gentoo-guys based on the
> 2.6.18-kernel that was part of Xen 3.1.3 (IIRC). It's _old_, really old,
> that's why it's hardmasked. The current 2.6.18-based Xen-kernel ebuild is
> the kernel (patch) that's included with Xen 3.3 (again, IIRC). There are no
> newer _official_ Xen-kernels (at least none newer than 2.6.18), and the
> Gentoo-developers decided not to include a forward-port anymore, as it
> quickly becomes unmaintainable when the version difference between kernel
> trunk and Xen kernel becomes larger.
> 
> There are forward-ports done by some other distributions (the 2.6.25 you're
> hinting at is the Xen-kernel forward port of the Debian-guys, IIRC).
> Someone is rebasing the SuSE-forward-ports of the Xen-kernels to Gentoo,
> and is offering ebuilds for download here:
> 
> http://code.google.com/p/gentoo-xen-kernel/downloads/list
> 
> The kernels offered by the SuSE-developers are at most 1-2 minor revisions
> behind the current vanilla kernel (as far as i can tell). I've been using
> those rebased SuSE-Xen-kernels productively on a Gentoo machine since quite
> some time, and they've always been very stable.

Hmmm for me it's quite ok to keep on with the 2.6.18 series, because i have
soooooooo much things to deal with the servers (my pipe is full twice ^^),
getting on the way with a new kernel compilation and having a downtime is no
more a possible thing as i've (for the moment, my pipe is full remember ?) no
backup servers for my dns/mail/etc... I'm just wondering if this can be a
security issue ? Or is the "productivity gain" good enough to motive me for
this, i take your words, pita ?

> 
>>   - is someone still working on Xen in Gentoo ?
> 
> Yes. To convince you, Xen 3.4.1 took about a day (post release by the Xen
> developers) to be included in ~x86-portage.

You're learning me something, i was not aware of such a release... This makes me
rethinking about the "productivity gain" of this new version ? I really love
having last versions of a software, if it implies a speedup...

> 
>>   - i know about kvm, so is there any reason to migrate to KVM instead of
>>   Xen ?
> 
> If you're currently using HVM, partially; HVM is in portage (and is also
> maintained), so you wouldn't need to rely on outside ebuilds, but the
> respective infrastructure for maintaining HVM-based machines from the
> command-line is poor (there's no such thing as xm and init-scripts, which
> can be a major PITA). If you're using para-virtualized kernels, then
> definitely no, as HVM fully virtualizes all I/O (which degrades disk-IO
> considerably more than a paravirtualized Xen instance), unless you're
> adventurous and willing to play with virtio-drivers, which I could never
> get completely stable.

I'm not using HVM at all. All my guests are Gentoo ones, so no need for this.
I'm using around one guests by provided services like name resolution, web
server, mail, etc, etc...

> YMMV, and HTH!

Until now, very good results with this architecture ! And this helped me, so
keep on going ;)

Many thanks.

--
      Xavier Parizet
YaGB :   http://gentooist.com
GPG  :    C7DC B10E FC21 63BE
B453 D239 F6E6 DF65 1569 91BF


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