请教kvm和hvm有什么区别 ?好在哪里

pika99

请教kvm和hvm有什么区别 ?好在哪里

lsylsy2

技术不同
理论上kvm性能更好
但hvm（准确说是xen hvm）胜在多年生产环境测试，稳定完善

pika99

KVM compared to Xen
Qemu, and, in effect, KVM and HVM Xen, use a particular kind of OS Image to boot a VM, which includes the kernel and a boot sector, similar to a bootable CD. This is different from a paravirt Xen OS image, which only includes the userspace parts of the OS image and is a raw copy of a volume with a root filesystem.
In KVM, a VM runs on top of a normal Linux kernel as a normal process. For example, using the 'kill' command on a KVM process kills the VM.
There is no logical network between the VMs and the VMM's physical network interface. This can be an advantage or a disadvantage:
There is less isolation between VMs and VMM, which can affect stability and security.
In terms of performance, it is hard to say if one approach is better than the other, but having a virtual network driver between VMs gives a performance penalty, and direct access to hardware is always faster. In both KVM and Xen it should be possible to bypass the driver domain (dom0 in Xen or the KVM VMM) and, with Xen paravirt, this has already been done, allowing VMs to have direct access to hardware. Bypassing the driver domain, however, is harder to implement in full virtualization (Xen HVM and KVM), although this may be solved with newer virtualization hardware extensions (e.g. VT-d).
KVM does not yet support SMP in VMs.
KVM is in the vanilla Linux 2.6.20 kernel and can be patched against older kernels. The source code profile of KVM is less intrusive on the kernel source and should be more easy to backport to older versions of Linux.
KVM relies on the availability of VT or SVM hardware extensions of x86 CPUs, which should be available in most new PC computers.

pika99

Xen HVM vs. KVM
Of course, if your machine supports virtualization in hardware, you might be inclined to wonder what the point of Xen is, rather than, say, KVM or lguest.

There are some excellent reasons to consider the idea. KVM and lguest are both easier to install and less invasive than Xen. They support strong virtualization with good performance.

However, KVM is, at the moment, less mature than Xen. It’s not (yet) as fast, even with the kernel accelerator. Xen also supports paravirtualization, whereas KVM does not. Xen PV offers a handy way of migrating domUs and a good way of multiplexing virtual machines—that is, expanding to a two-level VM hierarchy. Most importantly, though, Xen’s paravirtualized device drivers lead to much faster virtual machines—a feature that KVM, as of this writing, lacks.

Similarly, lguest is smaller, lighter, and easier to install than Xen, but it doesn’t support features like SMP or PAE (though 64-bit kernels are in development). Lguest also doesn’t yet support suspend, resume, or migration. Nonetheless, right now it’s difficult to say which is better—all of these technologies are out there being actively developed. If you are truly silly, you might even decide to use some combination, running Xen hypervisors under KVM, with paravirtualized domains under that. Or you might use Xen for now but keep your options open for future deployments, perhaps when HVM-capable hardware becomes more common. These technologies are interesting and worth watching, but we’ll stick to our usual “wait and see” policy.

Indeed, Red Hat has opted to do exactly that, focusing its development efforts on a platform-independent interface layer, libvirt, allowing (we hope) for easy migration between virtualization options. See Chapter 6 for more on libvirt and its associated suite of management tools

稀饭

一个是K开头一个是H开头

serverpoint

ekucn 威望         -2 引用 2011-4-14 23:01
喂扣分搞错位置了吧？

lsylsy2

原帖由 pika99 于 2011-4-14 23:05 发表


Xen HVM vs. KVM
Of course, if your machine supports virtualization in hardware, you might be inclined to wonder what the point of Xen is, rather than, say, KVM or lguest.

There are some excellent re ...
Xen的对比的KVM的HVM
当然，如果你的机器支持硬件虚拟化，你可能会倾向于不知道什么是Xen的一点是，而不是说，KVM或lguest。

有一些出色的原因，考虑这个想法。 KVM和lguest都更容易安装和不到Xen的侵入。他们支持与良好的虚拟化性能强。

但是，KVM是，目前，比Xen不太成熟。这不是（还）一样快，甚至与内核加速器。半虚拟化的Xen也支持，而KVM的没有。 Xen的光伏发电提供了一个方便的方式迁移多莫斯设计和良好的方式复用的虚拟机，也就是扩大到两级虚拟机的层次结构。最重要的是，Xen的半虚拟化设备驱动程序导致更快的虚拟机的一个功能式KVM，撰写本文时，所缺乏的。

同样，lguest更小，更轻，更易于安装比Xen的，但它不支持类似的SMP或PAE功能（尽管64位内核正在开发中）。 Lguest也还不支持暂停，恢复或迁移。不过，现在很难说哪一个更好，这些技术都是在那里正在积极发展。如果你是真正愚蠢的，你甚至可以决定使用一些组合，Xen的管理程序下运行KVM的半虚拟化与根据该域。或者你可以使用现在的Xen，但给你的选择未来部署，或许当的HVM能力的硬件变得越来越普遍开放。这些技术是有趣和值得关注，但我们将坚持一贯的“观望”的政策。

事实上，红帽已经选择了做抗争，集中在一个平台无关的接口层的开发力度，libvirt的，允许轻松迁移至虚拟化选项（我们希望）。见第6章关于libvirt的更多及其相关的管理工具套件