Technical specification analysis of OPENVZ and Xen of VPS providers at home and abroad

&http://www.aliyun.com/zixun/aggregation/37954.html ">nbsp; China IDC Market in recent years a good development, and a variety of new technologies and new products to the emergence of the IDC industry has injected new vitality, the early 2006 VPS (Virtual private server, VPN) into the Chinese market, with its unique advantages, the rapid occupation of the Chinese market, It has laid a good foundation for the development of our country's virtualization.

Compared with the virtual host, the VPS is more stable than the virtual host, while the price is cheaper than the exclusive host. Between stability and cost-effective, there are many enterprises and individual webmaster use VPS host. VPS Host Management is also more convenient than the virtual host, users in addition to the allocation of multiple virtual host and unlimited Enterprise mailbox, more independent server functions, you can install the program, separate restart the server. In other words, VPS is a highly resilient, high-quality and cost-effective server solution.

Ready to buy a VPS, compared to a number of VPS providers, foreign, domestic, pay attention to whether it is openvz good or xen good problem, then consulted some information, get some experience, share.

The following translation from Hostingfu.com,observer, I added a note.

Technical specification analysis of OPENVZ and Xen

The difference between 1.Xen and OpenVZ

Xen and OpenVZ are also virtualization host technologies, the difference being that Xen is a semi virtualization technology that is not a real virtual machine, but rather the equivalent of running a kernel instance, free to load kernel modules, virtual memory and Io, stable and predictable. OpenVZ is an operating system-level virtualization technology that is a layer of application on the underlying operating system, meaning easy to understand and low weight overhead, which generally means better performance.

There's a problem here and you can see that actually OPENVZ is better than Xen in theory because it eliminates a lot of public overhead. Why do we all think OpenVZ is too crushing? I think it is because OPENVZ configuration is more flexible, to the black-hearted OpenVZ service providers to change the opportunity to lower restrictions.

For example, Mediatemple, known as 512M Memory DV program, kmemsize only 12M, do not know people see 512M feel very ha ah, but when used in general this 512M can be divided into your hand half is good. This is a long way to go so that Xen can make better use of the illusion of machine performance.

2.OPENVZ Kernel model

First when the OPENVZ host says "256MB guarantee", it actually means about 232MB of "privvmpages", 14M of "kmemsize" and other miscellaneous resources. When the application calls malloc () the allocated memory will be added to "privvmpages".

When "privvmpages" exceeds the limit, malloc () fails and returns a null. When the host server is running out of memory, then the process in the virtual environment over "oomguarpages" will be terminated.

OpenVZ's memory management approach has both problems and advantages. One of the biggest problems is that memory-capacity applications use memory that is different from the memory the application actually allocates, and that the differences between applications can be significant. In Java, for example, it typically allocates a large chunk of memory, but it may use only a small fraction of the allocated memory. If Privvmpages is restricted, Java will stop running immediately. Tuning parameters can solve some of the problems, but it's handled absolutely without Xen. In fact, almost all applications that use memory allocations are affected by the OPENVZ problem.

/proc/meminfo itself has a problem. Although OpenVZ has been virtualized for memory, the "free" command still returns the host's memory. This makes small memory OpenVZ VPS Unable to run programs such as Java or GCC compilers.

The advantage of OpenVZ's memory model is that it's easy to understand: you're almost privvmpages limited. Unlike a dedicated server or Xen server, your disk cache and page caching do not count to your total memory usage. As a result, on a OPENVZ host that does not sell over, it may actually perform better than the same-specification Xen VPS Because of its large, redundant public resources.

3.Xen memory model

The Xen system model is easier to interpret. 256MB's Xen VPS is just like a 256MB dedicated server-the memory segment is reserved for VPS-only, no other VPS can use this part of memory, which is like a real dedicated server.

In addition, when memory is low, the VPS uses swap. Generally each VPS with twice times the size of the swap partition, when your application requires more memory, infrequently used pages from memory was swapped out to the swap partition, thereby freeing up more rooms. Therefore, the 256MB Xen VPS system actually has 768MB memory (256MB memory + 512MB swap space), please believe me, swap space is very useful, especially when dealing with unexpected peak demand.

So, Xen is always far superior to OPENVZ? Otherwise, your 256MB VPS theory can be used up to 768MB memory, while in fact the kernel, cache, buffer, they all occupy memory. This part of the system overhead is also considerable. In addition, swap can severely degrade performance.

4. Stability and predictability

Xen and OpenVZ behave differently when memory runs out. Xen swaps the infrequently used memory pages, which greatly reduces performance, and when swap is exhausted, the Xen system responds more and more slowly, like a real server.

And OpenVZ once ran out of memory, it will suddenly die: can not open a new program, only waiting for system resources available. What's more, the good programs that are supposed to run can also grow over the limit and suddenly die. This is like driving to 70 yards, and then suddenly hit the wall, the general will die miserably.

There is no doubt that I am inclined to Xen technology, predictable and stable.