OpenVZ Characteristics and Analysis

OpenVZ is open source software and is an operating system-level server virtualization solution based on the Linux platform. OpenVZ uses the core of SWsoft's Virutozzo virtualized Server software products, Virutozzo is the business virtualization solution provided by SWsoft Corporation.

OpenVZ can create multiple isolated virtual Private servers (VPS) on a single physical server and share hardware and management resources with maximum efficiency. Each VPS runs exactly the same as a standalone server, because its own users and applications can restart independently, and it has root access, users, IP addresses, memory, processors, files, app services, System library files, and configuration files. OpenVZ with lightweight process loss and efficient design is the best choice for running application services and real-time data production-based server virtualization.

The
• openvz is a virtualization technology based on the Linux operating system kernel, so only the OpenVZ virtualization technology can only be virtualized Linux systems
• The same reason, the host to the virtual machine "Partition" 512M of memory space, when the VPS boot, and will not be completely " Exclusive "host 512M memory, but how much to use, just can't exceed the limit." This kind of memory allocation to the service provider's "oversold" brings the possibility.
• connected, because the service provider gives you 512M of memory is only conceptually, so the real can give you the use of memory, depending on the service provider's reputation.
• openvz because of its own virtualization technology limitations, even for the Linux system, there are many kernel-related features do not work properly, such as the PPTP protocol VPN, Some functions of iptables firewall cannot be used properly.
• openvz Linux is not a swap partition, you can not partition the disk, etc.

In short, OpenVZ's host says "256MB guarantee", it actually means about 232MB "privvmpages", 14M "Kmemsize" and other miscellaneous resources. When the application calls malloc (), the allocated memory is added to "privvmpages". When "privvmpages" exceeds the limit, malloc () will fail and return a null. When the host server memory is exhausted, then the process in the virtual environment exceeds "oomguarpages" will be terminated.

OpenVZ's memory management approach has both problems and advantages. One of the biggest problems is the memory capacity of applications that use memory and applications that are actually allocated to memory that are different, and that the difference between different applications may be large. In Java, for example, it usually allocates a chunk of memory, but it may use only a fraction of the allocated memory. If Privvmpages is restricted, Java will stop running immediately. Adjusting the parameters can solve some of the problems, but it does not work with Xen cleanly. In fact, almost all applications that use memory allocation are affected by the OPENVZ problem.

/proc/meminfo itself is also problematic. Although the OpenVZ is already virtual for memory, the "free" command will still return the host's memory. This will make it impossible for small-memory OpenVZ VPS 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 only privvmpages constrained. Unlike dedicated servers or Xen servers, your disk cache and page cache do not count towards your total memory usage. Therefore, on a OPENVZ host that has no over-selling, it may actually perform better than the same-size Xen VPS Because of the large, redundant public resources.

OpenVZ Once the memory is exhausted, it will suddenly die: no new programs can be opened, only wait for system resources to be available. What's more, a good program that would have run may have exceeded the limit by growing and then suddenly died. It's like driving up to 70 yards, then suddenly hitting the wall and dying.

OpenVZ Characteristics and Analysis