KVM does not provide anywhere near the performance of OpenVZ (or Virtuozzo, its commercial equivalent). It's extremely important to note that KVM requires a running kernel inside the VPS, whereas OpenVZ runs containers using a shared kernel. This means that a 256MB KVM VPS does not actually have the same amount of memory available to userspace that OpenVZ does. OpenVZ is an extremely lightweight virtualization technology that easily outperforms full virtualization.
KVM does provide better isolation, although this isn't usually apparent to userspace in a container.
As for the original question, if I were shopping for a VPS, there are two factors to consider:
1) At the same price point, you'll get less for your money with KVM. 256MB of KVM is less than 256MB of OpenVZ because you have to run your own kernel so there's less for your actual applications. On the other hand, some hosters charge more for OpenVZ, so you'll need to do the math.
2) It's easier for hosting companies to overcommit OpenVZ systems, so bad hosting companies may put you on a system with too many containers, so be wary of this.
KVM has much better isolation than OpenVZ and in my experience KVM gets better performance as well. However I've heard some say they get better performance from OpenVZ. KVM has come a long way in the past year though, so I wouldn't be surprised if it's surpassed OpenVZ by now...
KVM also supports any operating system (in theory), whereas OpenVZ is limited to Linux only.
We're using KVM exclusively for our virtualization systems and have no interest in switching to anything else.
OpenVZ does not give your processes the full amount of allocated memory due to overhead, so for smaller memory VPSes, I would lean towards choosing KVM or XEN.
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KVM 无法提供与 OpenVZ（或 Virtuozzo，其商业同等产品）相媲美的性能。需要特别注意的是，KVM 需要在 VPS 内部运行内核，而 OpenVZ 使用共享内核运行容器。这意味着 256MB KVM VPS 实际上并不具有与 OpenVZ 相同的用户空间可用内存量。 OpenVZ 是一种极其轻量级的虚拟化技术，其性能可轻松超越完全虚拟化。
KVM 确实提供了更好的隔离，尽管这对于容器中的用户空间通常并不明显。
至于最初的问题，如果我购买 VPS，有两个因素需要考虑：
1）在相同的价格点上，使用 KVM 会得到更少的钱。 256MB 的 KVM 小于 256MB 的 OpenVZ，因为您必须运行自己的内核，因此实际应用程序的空间会更少。另一方面，一些托管商对 OpenVZ 的收费更高，因此您需要计算一下。
2) 托管公司更容易过度使用 OpenVZ 系统，因此不良的托管公司可能会将您置于具有太多容器的系统上，因此请对此保持警惕。
KVM does not provide anywhere near the performance of OpenVZ (or Virtuozzo, its commercial equivalent). It's extremely important to note that KVM requires a running kernel inside the VPS, whereas OpenVZ runs containers using a shared kernel. This means that a 256MB KVM VPS does not actually have the same amount of memory available to userspace that OpenVZ does. OpenVZ is an extremely lightweight virtualization technology that easily outperforms full virtualization.
KVM does provide better isolation, although this isn't usually apparent to userspace in a container.
As for the original question, if I were shopping for a VPS, there are two factors to consider:
1) At the same price point, you'll get less for your money with KVM. 256MB of KVM is less than 256MB of OpenVZ because you have to run your own kernel so there's less for your actual applications. On the other hand, some hosters charge more for OpenVZ, so you'll need to do the math.
2) It's easier for hosting companies to overcommit OpenVZ systems, so bad hosting companies may put you on a system with too many containers, so be wary of this.
KVM 比 OpenVZ 具有更好的隔离性，并且根据我的经验，KVM 也获得了更好的性能。不过我听说有人说他们从 OpenVZ 获得了更好的性能。不过，KVM 在过去的一年里已经取得了长足的进步，所以如果它现在超过了 OpenVZ，我也不会感到惊讶……
KVM 还支持任何操作系统（理论上），而 OpenVZ 仅限于 Linux。
我们专门将 KVM 用于我们的虚拟化系统，并且没有兴趣切换到其他任何系统。
KVM has much better isolation than OpenVZ and in my experience KVM gets better performance as well. However I've heard some say they get better performance from OpenVZ. KVM has come a long way in the past year though, so I wouldn't be surprised if it's surpassed OpenVZ by now...
KVM also supports any operating system (in theory), whereas OpenVZ is limited to Linux only.
We're using KVM exclusively for our virtualization systems and have no interest in switching to anything else.
如果您从 VPS 提供商处购买，则选择 KVM/Xen。 OpenVZ/LXC 供应商可能会超额销售其产品。
如果它是您自己的服务器，那么您可以在同一台计算机上混合使用 OpenVZ/LXC 和 KVM。
If your buying from a VPS provider, then KVM/Xen. OpenVZ/LXC suppliers can oversell their products.
If it's your own server then you can have a mix of OpenVZ/LXC and KVM on the same machine.
选择 KVM 因为 OpenVZ 通常比其他主机便宜:)
Choose KVM because OpenVZ is often cheaper to others hosts :)
由于开销，OpenVZ 不会为您的进程提供全部分配的内存，因此对于内存较小的 VPS，我倾向于选择 KVM 或 XEN。
OpenVZ does not give your processes the full amount of allocated memory due to overhead, so for smaller memory VPSes, I would lean towards choosing KVM or XEN.