VPS Hosting Stuff

Burstable RAM can be provided to users of Virtual Private Servers. Each Virtual Private Server has a guaranteed amount of RAM that it’s able to use at all times. At times it is possible that the usage may exceed the allotted amount of guaranteed RAM available, this is when Burstable RAM comes into play. Burstable RAM is provided to the user during times of high usage or traffic. This RAM is not in use by any VPS on a server and can be allocated to any VPS that may need it as long as it is available. So as long as those resources are available, you as a user will be able to go over that limit of guaranteed RAM.

In other words Burstable RAM is the RAM your VPS has the ability to use but it isn’t guaranteed to. Basically it’s for spikes in usage not consistent usage like Guaranteed RAM. For Example your if VPS has 384 MB Guaranteed RAM, and 1024MB Burstable RAM. This means that after you have used up your guaranteed ram, there is still 640MB Burstable RAM available for burst usage. For this reason we always keep some extra memory available on each server at all times as Burstable RAM.

Burstable RAM is never guaranteed to be available and should not be constantly depended upon for Virtual Private Server operation. If your VPS constantly requires greater resources than your package guarantees, we can quickly arrange an upgrade for you to a vps hsoting plan with greater guaranteed resources.

The Hardware Node requirements for the standard 32-bit edition of OpenVZ are :
1) Firstly, the computer should satisfy the Red Hat Enterprise Linux or Fedora Core hardware requirements.
2) IBM PC-A compatible computer is recommended.
3) CPUs: CPU used for VPS would be Intel Celeron, Pentium II, Pentium III, Pentium 4, Xeon, or AMD Athlon CPU. The more Virtual Private Servers you plan to run simultaneously, the more CPUs you need.

4) Memory: Minimum 128 MB of RAM. The more memory, the more Virtual Private Servers you can run. The exact figure depends on the number and nature of applications you are executing in your Virtual Private Servers. However, on the average, at least 1 GB of RAM is always preferable for every 20-30 Virtual Private Servers.

5) Hard Disk Drive: Minimum 4 GB of free disk space is recommended. Each Virtual Private Server occupies 400-600 MB of hard disk space for system files in addition to the user data inside the Virtual Private Server. It should be considered while planning disk division and the number of Virtual Private Servers to run.

6) NIC: Network card will be either Intel EtherExpress100 (i82557-, i82558- or i82559-based) or 3Com(3c905 or 3c905B or 3c595) or RTL8139-based are always preferable.A typical two-way Dell PowerEdge 1650 1u-mountable server with 1 GB of RAM and 36 GB of hard drives is suitable for hosting 30 Virtual Private Servers.

Following are some (possibly overlapping) representative reasons for and benefits of virtualization:

• Virtual machines can be used to consolidate the workloads of several under-utilized servers to fewer machines, perhaps a single machine (server consolidation). Related benefits (perceived or real, but often cited by vendors) are savings on hardware, environmental costs, management, and administration of the server infrastructure.
• The need to run legacy applications is served well by virtual machines. A legacy application might simply not run on newer hardware and/or operating systems. Even if it does, if may under-utilize the server, so as above, it makes sense to consolidate several applications. This may be difficult without virtualization as such applications are usually not written to co-exist within a single execution environment (consider applications with hard-coded System V IPC keys, as a trivial example).
• Virtual machines can be used to provide secure, isolated sandboxes for running untrusted applications. You could even create such an execution environment dynamically - on the fly - as you download something from the Internet and run it. You can think of creative schemes, such as those involving address obfuscation. Virtualization is an important concept in building secure computing platforms.
• Virtual machines can be used to create operating systems, or execution environments with resource limits, and given the right schedulers, resource guarantees. Partitioning usually goes hand-in-hand with quality of service in the creation of QoS-enabled operating systems.
• Virtual machines can provide the illusion of hardware, or hardware configuration that you do not have (such as SCSI devices, multiple processors, …) Virtualization can also be used to simulate networks of independent computers.
• Virtual machines can be used to run multiple operating systems simultaneously: different versions, or even entirely different systems, which can be on hot standby. Some such systems may be hard or impossible to run on newer real hardware.
• Virtual machines allow for powerful debugging and performance monitoring. You can put such tools in the virtual machine monitor, for example. Operating systems can be debugged without losing productivity, or setting up more complicated debugging scenarios.
• Virtual machines can isolate what they run, so they provide fault and error containment. You can inject faults proactively into software to study its subsequent behavior.
• Virtual machines make software easier to migrate, thus aiding application and system mobility.
• You can treat application suites as appliances by “packaging” and running each in a virtual machine.
• Virtual machines are great tools for research and academic experiments. Since they provide isolation, they are safer to work with. They encapsulate the entire state of a running system: you can save the state, examine it, modify it, reload it, and so on. The state also provides an abstraction of the workload being run.
• Virtualization can enable existing operating systems to run on shared memory multiprocessors.
• Virtual machines can be used to create arbitrary test scenarios, and can lead to some very imaginative, effective quality assurance.
• Virtualization can be used to retrofit new features in existing operating systems without “too much” work.
• Virtualization can make tasks such as system migration, backup, and recovery easier and more manageable.
• Virtualization can be an effective means of providing binary compatibility.
• Virtualization on commodity hardware has been popular in co-located hosting. Many of the above benefits make such hosting secure, cost-effective, and appealing in general.
• Virtualization is fun.
• Plenty of other reasons …

A virtual private server (VPS, also referred to as Virtual Dedicated Server or VDS) is a method of partitioning a physical server computer into multiple servers such that each has the appearance and capabilities of running on its own dedicated machine. Each virtual server can run its own full-fledged operating system, and each server can be independently rebooted

The practice of partitioning a single server so that it appears as multiple servers has long been common practice in mainframe computers, but has seen a resurgence lately with the development of virtualization software and technologies for other architectures.

OVERVIEW

The physical server boots normally. It then runs a program that boots each virtual server within a virtualization environment (similar to an emulator). The virtual servers have no direct access to hardware and are usually booted from a disk image.

There are two kinds of virtualizations: software based and hardware based. In a software based virtualization environment, the virtual machines share the same kernel and actually require the main node’s resources. This kind of virtualization normally has many benefits in a web hosting environment because of quota incrementing and decrementing in real time with no need to restart the node. The main examples are Xen,Virtuozzo, HyperVM, Vserver, and OpenVZ which is the core kernel of both Virtuozzo and HyperVM.

In a hardware based virtualization, the virtualization mechanism partitions the real hardware resources. In typical implementations, no burst and/or realtime quota modification is possible; the limits are hard and can only be modified by restarting a virtual machine instance^{[citation needed]}. This kind of environment is potentially more secure in the sense that it is less subject to “Quality of Service crosstalk” between VM instances^{[citation needed]}; on the other hand, its security is typically dependent on the correctness of a larger and more complicated Trusted Computing Base^{[citation needed]}. It is more commonly used in enterprise/commercial deployments^{[citation needed]}. Examples include Microsoft Virtual Server, VMware ESX Server, and Xen.

USES

Virtual private servers bridge the gap between shared web hosting services and dedicated hosting services, giving independence from other customers of the VPS service in software terms but at less cost than a physical dedicated server. As a VPS runs its own copy of its operating system, customers have superuser-level access to that operating system instance, and can install almost any software that runs on the OS. Certain software does not run well in a virtualized environment, including firewalls, anti-virus clients, and indeed virtualizers themselves; some VPS providers place further restrictions, but they are generally lax compared to those in shared hosting environments. Due to the number of virtualization clients typically running on a single machine, a VPS generally has limited processor time, RAM, and disk space.

Due to their isolated nature, VPSes have become common sandboxes for possibly-insecure public services or update testing. For example, a single physical server might have two virtual private servers running: one hosting the production-level (live) website, and a second which houses a copy of it. When updates to crucial parts of software need to be made, they can be tested in the second VPS, allowing for detailed testing to be conducted without requiring several physical servers.

Virtual private servers are also sometimes employed as honeypots, allowing a machine to deliberately run software with known security flaws without endangering the rest of the server. Multiple honeypots can be quickly set up via VPSes in this fashion.

Virtual private server hosting

A growing number of companies offer virtual private server hosting, or virtual dedicated server hosting as an extension for Web hosting services. Some web hosting companies call a Virtual Private Server a Virtual Dedicated Server/Dynamic Dedicated Server or the other way around.

Managed Hosting

Tools are provided to monitor and control the virtual machine.

Unmanaged Hosting

Typically only minimal services are provided, such as ssh console and reboot. Unmanaged VPS hosting is generally less expensive than managed VPS hosting.

Unmetered Hosting

Similar to unmanaged hosting but a fixed bitrate is offered so that it is not possible to exceed a monthly budget.

Virtualization software

For some of the software packages commonly used to provide virtualization, see comparison of virtual machines.

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Above info received from :-http://en.wikipedia.org/

Nice discussion going on slashdot.org about performance differences of xen and openVZ.

An anonymous reader writes Compared to an operating-system-level virtualization technology like OpenVZ, Xen — a hypervisor-level virtualization technology that allows multiple operating systems to be run with and without para-virtualization — trades off performance for much better isolation and security. OpenVZ’s performance advantage due to running virtual containers in a single operating system kernel can be significant. A performance evaluation study (PDF) done by researchers at the University of Michigan and HP labs provides insight into how big a performance penalty Zen pays and what causes the overheads (primarily L2 cache misses).

From the report: “We compare both technologies with a base system in terms of application performance, resource consumption, scalability, low-level system metrics like cache misses and virtualization-specific metrics like Domain-0 consumption in Xen. Our experiments indicate that the average response time can increase by over 400% in Xen and only a modest 100% in OpenVZ as the number of application instances grows from one to four… A similar trend is observed in CPU consumptions of virtual containers.”

Read more from : http://slashdot.org/article.pl?sid=07/05/15/019251

Virtualization is a framework or methodology of dividing the resources of a computer into multiple execution environments. Virtualization techniques create multiple isolated partitions — Virtual Machines (VM) or Virtual Environments on a single physical server.

Techniques:

There are several kinds of virtualization techniques which provide similar features but differ in the degree of abstraction and the methods used for virtualization.

Virtual machines (VMs)

Virtual machines emulate some real or fictional hardware, which in turn requires real resources from the host (the machine running the VMs). This approach, used by most system emulators, allows the emulator to run an arbitrary guest operating system without modifications because guest OS is not aware that it is not running on real hardware. The main issue with this approach is that some CPU instructions require additional privileges and may not be executed in user space thus requiring a virtual machines monitor (VMM) to analyze executed code and make it safe on-the-fly. Hardware emulation approach is used by VMware products, QEMU, Parallels and Microsoft Virtual Server.

Paravirtualization

This technique also requires a VMM, but most of its work is performed in the guest OS code, which in turn is modified to support this VMM and avoid unnecessary use of privileged instructions. The paravirtualization technique also enables running different OSs on a single server, but requires them to be ported, i.e. they should “know” they are running under the hypervisor. The paravirtualization approach is used by products such as Xen and UML.

Virtualization on the OS level

Most applications running on a server can easily share a machine with others, if they could be isolated and secured. Further, in most situations, different operating systems are not required on the same server, merely multiple instances of a single operating system. OS-level virtualization systems have been designed to provide the required isolation and security to run multiple applications or copies of the same OS (but different distributions of the OS) on the same server. OpenVZ, Virtuozzo, Linux-VServer, Solaris Zones and FreeBSD Jails are examples of OS-level virtualization.

Short comparison

The three techniques differ in complexity of implementation, breadth of OS support, performance in comparison with standalone server, and level of access to common resources. For example, VMs have wider scope of usage, but poor performance. Para-VMs have better performance, but can support fewer OSs because of need to modify the original OSs.

Virtualization on the OS level provides the best performance and scalability compared to other approaches. Performance difference of such systems can be as low as 1…3%, comparing with that of a standalone server. Virtual Environments are usually also much simpler to administer as all of them can be accessed and administered from the host system. Generally, such systems are the best choice for server consolidation of same OS workloads.

Source: http://wiki.openvz.org/Introduction_to_virtualization