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I am aware of the multitude of virtualization threads here but they all seem to be oldish and i'd like to have a brand new one ready for 2012.

I'm currently evaluating Xen, OpenVZ and KVM for virtualization purposes. I'm having trouble deciding what to use. The OS this will be running off of is Debian, preferably. The guest OS's will all be *nix based, mostly Debian as well. No windows, macos or other exotic stuff required. I have a single server, which has 16gigs of ram and a xeon processor on it. I also have a software raid 1 disk configuration with 3tb raid capacity.

I am setting up this environment so separate the sites my current server hosts by level of trust, and software version. For example, there are some sites i know might have security holes, others which should be perfectly secure, and others that require an archaic version of PHP.

All in all, i'd like to set up 3 different guests: one for trusted, one for untrusted, one for old php.

Part of my problem is managing backups properly: I enjoy using Bacula or duplicity to manage my backups because of incremental, encrypted backups. I do not want any of my client sites to ever have to go offline due to backup processes. I also only have 100 gigs of remote off-site backup space, so i want to use that wiseley, and not just dump all i have up there. Restoring from backups should be fast [no downloading huge iso files!].

I also want to do the disk space allocation right. I've read marvelous things about LVM and how it makes ones life easier. Assuming a raid 1 [two 3tb disks under raid1], how would you lay out your partition map?

I'd be happy if somebody could share his personal experiences, setup configurations and win/fails regarding different virtualization platforms, for a similar goal as mine.


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2 Answers

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I'd say use KVM - that way your hypervisor & Dom0 can be the standard debian you're familiar with. With KVM, the hypervisor and the Dom0 are the same machine - it's one of the design principles behind KVM that the best hv to have is a full-featured linux system.

With Xen, the hypervisor runs on the bare metal and the Dom0 runs inside it along with all the guest DomUs, kind of like a special purpose VM.

I don't think container-style virtualisation offers enough real benefits over simple vhosting that it's worth the bother.

For performance, I think your plan to use LVM for VM images (rather than, say, image files on a fs) is a good one.

Alternatively, you could use zfsonlinux (note: not zfs-fuse, it's too slow) which is pretty stable and reliable. the "catch" is you have to download the debianised source packages from the ubuntu zfsonlinux PPAs and recompile them for debian. easy if you're comfortable with compiling packages, probably not very easy if you're not.

zfs gives you everything that LVM with fewer restrictions and limitations (e.g. snapshotting even running VM volumes is fast and easy), and with a much less steep learning curve. If you're already familiar with LVM that last one isn't a big deal.

Disclaimer: I'm opinionated and therefore biased.

I'm not a fan of Xen. I've used Xen & KVM, dabbled with vmware (and virtualbox too although that's more of an end-user/desktop-oriented virtualisation tool rather than server virtualisation) and I strongly prefer KVM. It just works, without stupid hassles.

I'm hoping that the recent merge of Xen into the mainline kernel results in rapid improvement of Xen. It certainly can't hurt to escape being stuck with ancient kernel versions.

similarly, i'm not a huge fan of LVM either. I used it in the past because there was nothing else that did what it did. However, I have never liked it and have always thought that it is clumsy and obtuse and gratuitously complicated. i've been using zfsonlinux for a few months now and it's everything i ever wanted LVM to be. I hope i never have to build or administer another lvm system again.

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Thanks for the input. I've gone ahead and set up KVM+libVirt+qemu and i'm using two virtual debian machines already. It seems quite simple and straightforward. I'll take a look at using zfsonlinux too. –  elmariachi Nov 10 '11 at 21:14
I would agree with using KVM for this, KVM includes the KSM service which does memory deduplication on the fly. If all of your VMs are going to be running very similar OSes then this will really help. –  n8whnp Nov 12 '11 at 15:42
-1 Saying that containerization has not enough more benefits than vhosting is not well explained and simply not right. Containers isolate memory, network, disk, processes, and system resources. There are many benefits to that. Example: one of your web interfaces has a remote vulnerability that gives shell and there is a local vulnerability that escalates to root. Your kernel is up to date. In this case all your other services which are in different containers are protected. With vhosts your entire machine would be f'ed. For Xen vs OpenVZ pref. please see wiki.openvz.org/Performance –  Aleksandr Levchuk Nov 13 '11 at 19:11
it's not up to me to explain the benefits of a technology that i don't use, especially when i clearly stated (and clearly identified it as just an opinion, not claimed it as objective fact) that i don't think it's worth the bother (in my experience, it's more effort than running kvm or xen VMs). if YOU think container VMs are worthwhile, then write your own answer extolling their virtues rather than just lazily downvoting an answer because you disagree with one sentence. this site benefits from lots of people sharing their different experiences. group-think agreement is not mandatory. –  cas Nov 14 '11 at 8:51
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You should also give a try to LxC (Linux Containters) which offers an OS-level Virtualization like OpenVZ but supported in the mainline Kernel. This technique might be preferable to you because you can expect an higher density (more "virtual machines" than with KVM / Xen).

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Thank you for your mentioning of LxC, i didnt know about it. Yet, i'm more interested in finding out the setups that people use, than in knowing that there is "yet another technology available". Furthermore, im interested in the various advantages of a specific soultion in regard to the backup aspect. –  elmariachi Nov 9 '11 at 12:30
LxC was well behind OpenVZ in March 2010. I don't know if that changed over the year. Please see openvz.livejournal.com/30998.html?thread=97046#t97046 –  Aleksandr Levchuk Nov 13 '11 at 19:17
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