This question is the one many people ask themselves before purchasing their first VPS. Indeed, when you only check out the plans, you cannot tell for sure what intensity of RAM usage you expect. What you know, is the approximate amount of physical memory used by the software you are going to run on your VPS. Software system requirements, however, are usually not enough to estimate the real use of RAM needed for the particular application or script to operate, and thus it is hard to know how much physical memory the entire server with all its background processes in general is going to need.

There are some facts that you know that might help you there. For instance, we know that the server in its basic installation – usually LAMP – requires at least 128 MB of RAM. Choice of the control panel will make you add another 64 MB to your requirements (if your choose WebMin or DirectAdmin) or even 128 MB – if you want to run cPanel. This makes a minimum of 256 MB with a lack of operating options. What you can run there is email and FTP exchange (not intensive though) and hosting of simple websites. Dynamic and script-driven websites, such as CMS will also fit this configuration but you may need to implement many adjustments, some of which can limit the functionality of your online project.

If you look into running something more serious on the Web, you will need to search for a more solid solution. Let us review bigger VPS configurations and estimate what can be hosted there.

512 MB

This is one of the most popular configurations available on the market of VPS hosting. A VPS with 512 MB of RAM usually becomes a step-up for users who have never dealt with VPS servers before and who gave this type service a try on a smaller plan and then requested an upgrade.

If you want to host E-commerce software or run a script that is going to use your server resources constantly – a VPS with 512 MB of RAM is going to suit you perfectly. This plan will also fit those, who look into using a VPS as a platform for hosting reselling – simple shared hosting, of course. WordPress and Magento users will also find such a VPS a better luck, since 256 MB virtual machines never let them run those CMS full-throttle.

1024 MB

A one-Gig VPS is a choice of a Pro. Many gurus and experienced webmasters, as well as resellers and other online business holders, either purchase those servers at once or upgrade to them shortly.

If you deal with hosting reselling, you will find a VPS with 1024 MB RAM to be a perfect solution for serious reseller business. Unlike smaller VPS plans, those and higher let you offer the so-called Master reseller hosting which implies that your resellers will be able to sell hosting, too. And of course, a more powerful VPS will let you manage the clients easier. Indeed, if you have a thousand clients or more, whatever the business you do is, why should you partition them into groups to send emails hourly so as not to overload the server. You deal with e-commerce, so you must have some special offers and discounts and you want to be sure, everyone knows it – a powerful VPS will let you notify everyone at once without overloads or any other issues.

2048 MB

If you need a power of a dedicated server, but do not want to pay extra for the features you do not need, a 2 GB VPS is something you will like.

Those servers are usually the top ones among many VPS hosting providers and thus have the highest privileges on the carrier. This feature will make you feel absolutely comfortably on your VPS and it is worth it. Such a powerful VPS is heaven for big online projects and geeky things – those servers are capable of letting you refuse from standard server configuration, so one can easily install there such popular software as Java, Tomcat webserver, FFMPEG and many other tools, to make their online project a hi-tech multimedia pad.

We hope that this review of the most popular VPS plans helped you find out what you need or may need for your online business. If it did, you may like the news that since recently we run a special offer that has doubled RAM on all our VPS servers, so now our 256 MB, 512 MB and 1024 MB plans come with 512, 1024 and 2048 Megabytes of RAM accordingly.

After we have delivered you numerous articles on different aspects of VPS hosting, we’ve noticed that we need to get back to this topic again. Once again we are going to talk about the problem of choice of a VPS server. This time we are going to take a look at this question under a different angle – let us share some interesting tips on how to tell if what you see when checking out the feature/pricing page of your potential VPS host is what you are going to get. While introducing you choice-making tips in our previous articles we usually referred to the technical aspect of VPS hosting, today we are going to analyze the VPS hosting from the point of view of a customer.

How much RAM do you get in fact?

When you see a 1 GB VPS plan at a very low cost, don’t be too fast in making optimistic conclusions. Check if this entire amount is guaranteed RAM. The best option is to contact sales support – then you are going to have a proof – a copy of your chat or email. But if you don’t have time for those checks, there is a quick way to find it out on your own – check the virtualization type used by this host. If it is XEN – be sure the entire 1 GB of RAM is guaranteed. If they use OpenVZ (the hosts that use it often say their VPSes are powered by Virtuozzo), there’s a risk, that their pricing provides the combined amount of RAM – guaranteed + burstable (RAM, that may be allocated only for a short period of time and thus – not constantly available). Since RAM is the main feature of any VPS server, this should one of the first points you verify before moving any further.

CPU units

Checking out pricing of some VPS hosts, one can find such feature as CPU units. This parameter shows the CPU frequency, available for the given VPS. Although it looks rather informative and lets the potential client compare the offered plans in more details, it’s not quite a correct way to represent VPS CPU specifications. To find out how powerful the CPU of the given VPS is, you need to know, what number of cores the entire VPS-carrier has, what their frequency is and how much of this power is delegated to the specific virtual machine – the latter factor depends on performance priority.

If you don’t know, how to interpret this information, you can simply ignore it. If you do need the details, you can have a brief consultation with the sales department of your potential host. This will let you find out the specifications of the carrier. The more powerful it is and the bigger the plan you are looking into, the more powerful your VPS is going to be.

Disk Space

Since VPS servers are usually offered as a fast solution that is cheaper than a dedicated server, those are not designed for large data processing. The minimal plan at some VPS hosts may offer as little as 10 GB of disk space. If you are going to host a few web pages, it’s alright, but if you work with email and databases, you need to consider disk space allocation rather carefully. Now let us count what you have in the end – after your server is setup, the system may take up to 2 GB of disk space. Any backup you make is going to create a file of the size approximately equal to the size of your /home directory. Not that much space left, isn’t it? That is why another Gigabyte of your virtual HDD may become vital. Well, it can also be taken by swap. According to the architecture of OS Linux, swap is a fixed disk partition, not a file, unlike on Windows – therefore, before you order a XEN-based VPS, you need to consult sales department first, to find out whether /swap is counted with the disk space offered or not.

Summary

If you want to be completely sure about your future VPS host, you need to find out as many details as you can before you actually sign-up for their services. Your potential host may not list everything on their web-page, it’s alright, but their sales and technical team should always be able to explain these or those aspects of hosting with their company. If it happens that some of your questions remains unanswered, you have serious reasons to not consider this host. If you are looking for an affordable and reliable VPS host right now, please spend another minute checking out our plans here at SiteValley.com.

Web hosting control panel is a set of tools and interfaces designated to maintain and monitor a hosting account. On shared and reseller hosting plans such panels are installed and configured by a provider company. Depending on the type of VPS and Dedicated server, control panel software can be either pre-installed or be absent at all. The main advantage of using a control panel is the ability to control your account via a comfortable web based graphical user interface, which, in turn, means that you do not need to possess any knowledge of OS specific console commands to maintain your hosting. Control panels features normally include (but are not limited to):

• Viewing server logs
• Monitoring quotas usage (e.g. disc space, bandwidth, mail accounts, ftp accounts etc.)
• Working with e-mails (creation, modification, termination and checking of e-mail accounts, modification of MX records, autoresponders, forwarders and many more)
• Managing FTP accounts
• Managing domains, addon domains, subdomains and parked domains.
• Managing databases
• Collecting and viewing web statistics (e.g. visitors, pageviews etc.)
• Working with files of the hosting account (using a web based file manager)

A fast and feature rich webhosting control panel can significantly increase both productivity and quality of any online business or project. Webmasters obtain impressive management tools for performing most crucial administrative procedures for every day account operations with the help of it. In absence of an efficient hosting control panel every webmaster and user would need an extensive internet and OS administration training in order to effectively use their hosting accounts. There are many control panels these days (you can find a list of 4 famous ones at http://webhostingrating.com/articles/2009/12/4-most-influential-control-panels/ ), but not all of them are as popular and widely used as cPanel and Direct Admin. This is mostly due to the unique set of features and capabilities included in the latter two. Although cPanel has a Windows platform version as of today, both cPanel and DirectAdmin are normally regarded as Unix OS designated.

Webhosting cPanel software

cPanel is considered to be the most popular control panel. This is the first name that will likely occur when talking about “control panels”. Apart from being very famous, it is also a rather complex piece of software. Webhosting cPanel has conquered such a huge part of today’s panels market that its main advantage appears to be its own popularity. Since there are so many users operating cPanel, the amount of online tutorials, guides, community discussions and solutions to various issues is humongous. Another outstanding point about it is it’s abundance of expandable features. Anything that can be done with hosting is either directly implemented into cPanel already or can be added as addon. On the other hand, the complexity of this panel creates limitations on the minimal system requirements. Low server hardware parameters and lack of appropriate configuration can cause significant slow downs and even restarts of the panel itself.

Direct admin control panel

While cPanel is known to be one of the most sophisticated and feature rich panels, DirectAdmin is known for its extreme user friendliness and simplicity. The well written C/C++ code of DirectAdmin makes it one of the fastest and least resource hungry panels. This panel includes most necessary features sufficient for efficient and comfortable account management. It is thought to have fewer bugs and is regarded more stable than cPanel due to a finer code and shorter list of functions. Direct admin is most often used as a control panel for shared solutions due its lower cost and higher stability.

cPanel vs DirectAdmin

Let’s take a look at regular user interfaces of both panels:

cPanel Control Panel Home Menu

Direct Admin Control Panel Home Menu

From the above screenshots you can see that the amount of information presented in home menu of cPanel is larger than that of a DirectAdmin. A newbie user may get confused by all the unknown buttons and sections, but things are not as complicated in cPanel as it may seem from the first look. All actions are divided into corresponding sections, making searching for menus easy. These menus are:

• Preferences
• Mail
• Files
• Logs
• Security
• Domains
• Databases
• Software/Services
• Advanced

There sections can be collapsed and expanded in order to free up space in your cPanel. One of the inconveniences is a large amount of menus a user has to go through in order to find the button he needs. For faster locating of options there is a handy search bar integrated at the top of left sidebar in cPanel.

Direct Admin power user interface is split into three main sections: “Your account”, “E-mail management” and “Advanced Features”. Most of the basic account management features such as domain setup, FTP management, MySQL management, File Manager and other are located in the “Your Account” section. This eases up the search and implementation of changes for a user. All the e-mail related activities are done in the corresponding “E-Mail Management” section. This is the only place a normal user would have to go to in order to apply changes to his/her email configuration when using Direct admin web host control panel. The more advanced tasks, such as configuring cron jobs, apache handlers or installing applications using a 1-click installer are located in the “Advanced Features” sections.

Lower level menus such as FTP account setup for example look very similar in both control panels:

Lower level menus structure comparison (cPanel and Direct Admin)

Both hosting control panels have PHPMyAdmin for advanced database management, as well as one click installers and online website builders as additional addons.

There are numerous discussions about the speed advantage of DirectAdmin over cPanel (see http://www.webhostingtalk.com/showthread.php?t=852355 for example), but it is quite hard to determine just how much faster Direct Admin truly is. This is so because such a conclusion can be drawn only from testing results performed under equal conditions on similar production servers with real clients.

Bottom Line

Overall we can conclude that cPanel features list is larger than that of the Directadmin. Almost any hosting related task can be performed using cPanel’s GUI. On the other hand, some advanced administration actions can be done only via a console in DirectAdmin. cPanel is an older control panel, which, in result, is more widely used and supported by community. This means it’s easier to find free tutorials, recommendations, fixes and free community support for cPanel.

As far as Directadmin is concerned: it is written in a cleaner code due to the fewer features implemented in it. This makes it less demanding for resources and faster in functioning. The GUI of Directadmin is more suitable for beginner and medium level users. Nevertheless, all features crucial for hosting account management are present and can be easily accessed through Directadmin. A distinctive property of this panel is its relatively low price: some Directadmin licenses cost twice less than those of cPanel.

On all shared plans at Sitevalley.com we provide preinstalled and preconfigured DirectAdmin web hosting panel. This ensures significant speed increase as compared with cPanel and impressive reliability for all users on the shared servers. At the same time, we also provide cPanel webhosting control panel on our VPS servers for full control and monitoring of your account with us. We also offer DirectAdmin control panel on our Dedicated Server plans for free.

Virtualization is a widely used technology nowadays. A whole set of hosting plans is based on it – the so-called Virtual Private Servers (VPS). They allow steady transition from regular shared to the most powerful dedicated solutions. While big projects may require the power of an independent dedicated server, some personal and small-to-medium businesses may not need such resources at high costs at first. At the same time the needs of  such customers may not be satisfied with what regular shared hosting has to offer due its nature . Unlike shared hosting, V PS allows full isolation from other users on the host server. It provides full control over the account (i.e. root access), remote reboots and system restore.

Nowadays various approaches and implementations of virtualization exist. In this article we will compare two most widely used virtualization engines: OpenVZ and Xen. The main goal of the article is to provide basic concept, and outline the differences and similarities of the two engines.

Virtualization

As defined by Wikipedia virtualization is a term that refers to the abstraction of computer resources. In case of VPS  hosting plans, platform virtualization is used. Its idea is to separate an operating system (OS) from hardware it is being run on. With no virtualization applied, normally only one operating system can be run on one set of hardware at the same time. As depicted in the Figure 1, every server composed of a definite hardware set can simultaneously run only one OS, however, if the virtualization technology is applied, one achieves the ability to have numerous OSs run on single set of hardware at the same time:

Figure 1. Application of virtualization. Source: http://mysite.stonybrook.edu/

As we can see, the virtualization is used to create an independence from the hardware for an OS. Virtualization software not only allows to run several OSs on the hardware, but also separates the resources a single OS is consuming. This way various quotas for CPU, RAM, HDD I/O and such can be defined for a single OS. Quota based isolation increases the utilization of a single dedicated server by dividing resources of the latter into smaller chunks. This is quite efficient as it decreases the cost of a single VPS and, at the same time, provides new unique features to the user.

Paravirtualization

In order to understand how virtualization works let’s consider its structure (see  Figure 2 ). As we can see form the figure, main idea of virtualization is creating a special interaction layer (Virtualization layer) between the hardware and OS which acts as a resource isolator and manager at the same time:

Figure 2 Basic structure of virtualization. Source: http://desktop-virtualization.com

Figure 2 shows a special case when the virtualization layer is placed directly on top of the hardware (architecture) and then the OSs are installed on top of the virtualization layer. Consequently, the applications such as Apache Web Server and MySQL server are run on top of the OS and do not interact with the applications run on the other OSs. This way the depletion of resources given to one OS does not influence the performance of the other OSs on the hardware carrier server. Such isolation eliminates the possibility of overloads caused by other users on the carrier. This kind of virtualization can be referred to as to a Paravitualization.

As defined by Wikipedia paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar but not identical to that of the underlying hardware. This technique is used in the XEN virtual engine. Paravirtualization has a number of limitations, one of which being a special need for slight modification of the OS kernel in order to teach it to use the instructions given by virtualization layer. Such need, however, can be avoided by utilization of special processors supporting the hardware assisted virtualization technology. A processor with such capability can help the software virtualization layer to perform the abstraction. This way no modification is required to be performed to the OS, and therefore any proprietary software like Microsoft Windows can be run on the virtualization layer. Not only it allows for running of proprietary technologies, but it also lets using the original form of the OS which can be important for a number of applications run on it.

Operating system-level virtualization

Paravirtualization is not the only type of the virtualization used in hosting industry. Another widely used type is Operating system-level virtualization (OSLV). This kind is defined In Wikipedia as a method where the operating system allows for multiple user-space instances (virtual hosting, chroot jail + resource management). This means ,that only one OS with only one kernel is running on the server. OS is modified in such a way that it allows for creation of so-called containers which appear as a separate OS entity to the user and software within that container. This can be depicted as shown in the Figure 3:

Figure 3 Basic structure of Operating system-level virtualization. Source: http://www.linux-watch.com

This type of virtualization is implemented in the OpenVZ engine. Resource sharing in such structure differs from the paravirtualization. In the latter technology the resources are firmly distributed on the virtualization level, and no sharing takes place. In the OSLV all containers (VPSs) are running in the same environment. The resources of each one are assigned and limited. However, there is a certain amount of the resources that is kept for sharing within the host OS and is not assigned to any specific VPS. If such resources are not occupied by host system, any VPS can use them if necessary. An example can be given in terms of a burstable RAM. There is a guaranteed RAM quota VPS always has, and there is also a top limit of burstable RAM this VPS can also use in case the system has any additional free RAM besides the amount already guaranteed and provided.

In OSLV all containers run inside a single host system. Each container emulates an OS within itself, but it can only emulate the OS kernel which is similar to the one the container itself is running in. This is a great limitation. OpenVZ is run on Linux OSs. Therefore, the only OS that can be installed in the containers within the carrier is of Linux. This way usage of FreeBSD is simply not possible within the OpenVZ based VPS. At the same time, there is no problem using FreeBSD in a paravirtualized environment like Xen.

Xen vs OpenVZ

Xen

Figure 4 Xen paravirtualization architecture. Source: http://uberhip.com

Xen is a virtualization engine (to be exact it is a virtual-machine monitor) for x86, x86-64, Itanium and PowerPC platforms. On number of processor a paravirtualization technique is applied by Xen. This means that the operation systems run on Xen are modified in order to achieve high performance on a wide range of hardware architectures, which are initially not intended for virtualization technologies. The architecture of Xen is presented in Figure 4.

Xen uses one privileged OS to control the hardware resources. This privileged OS must be a Unix based one (e.g. Linux, FreeBSD etc.). In the latest versions of Xen the following OSs can be run as guest ones:Linux, Minix, Plan 9 from Bell Labs, NetBSD, OpenBSD, FreeBSD, OpenSolaris, NetWare, GNU/Hurd/Mach, OZONE.

OpenVZ

Figure 5 OpenVZ operating system-level virtualization architecture. Source: http://www.linux-watch.com

OpenVZ is an open-source virtualization engine on the x86, x86_64, and IA64 processors. OpenVZ, itself, is built on top of Linux. Unlike Xen’s paravirtualization technique, with OSLV virtualization the operating environment is virtualized instead of the hardware. Thus, while there is only one operating system kernel, multiple programs run in isolation from each other within the single OS instance. The basic architecture of OpenVZ is shown in the Figure 5. OpenVZ project manager Kir Kolyshkin said in a statement about its architecture:

“Unlike hypervisor-based virtualization technology [such as Xen and VMware], OpenVZ is extremely easily portable across different architectures, since 95 percent of the code is platform-independent. With the port to Power, we’ve opened the door for another segment of the user community to benefit from our open source virtualization software”.

Differences and Similarities.

Both system present the user with the following benefits:

• consolidation
• increased utilization
• rapid provisioning
• dynamic fault tolerance against software failures (through rapid bootstrapping or rebooting)
• hardware fault tolerance (through migration of a virtual machine to different hardware)

Resources

Additionally both Xen and OpenVZ provide the the ability to securely separate virtual operating systems. However, this feature is implemented through different techniques in these two virtualization solutions. Xen provides full fixed isolation, where the initially assigned quotas are kept throughout the entire functioning period, and additional request for memory are processed using the swap space on the HDDs. OpenVZ ,on the other hand, provides semi-dynamical assignment of resources. Such terms as burstable RAM and resources exist on OpenVZ. Therefore, unlike the case with Xen, VPSs based on OpenVZ may also take advantage of the free resources of the server. This can result in better utilization of the resources of the carrier hardware.

Performance

The virtualization overhead observed in both OpenVZ and Xen is limited. Various opinions exist on the difference in performance between the two. However, in both cases the performance levels of virtualized environment, as compared to the real hardware, are of acceptance-quality level. Specific figures depend on a great number of factors and cannot be summed up for the general conclusion.

Compatibility

Unlike OpenVZ, XEN has the ability to support legacy software as well as new OS instances on the same computer. That means that proprietary systems can be installed on Xen based carrier without any additional modification if hardware assisted virtualization is used. OpenVZ provides compatibility only in frame of the alike kernel, such as various distributions of Linux OSs.

Migration

Both provide great and relatively equal check pointing and live migration options.

Scalability

Both engines are based on the Unix OSs, therefore they have great scalability. For example in case of OpenVZ which employs a single kernel model, it is as scalable as the Linux kernel. Such kernel supports up to 64 CPUs and up to 64 GB of RAM. (on 32-bit with PAE) A single container can scale up to the whole physical system, i.e. use all the CPUs and all the RAM.

Management

Peculiarity of OpenVZ is the mass management support. An administrator (i.e. root) of an OpenVZ physical server (carrier) can see all the running processes and files of all the containers on the system. That makes mass management scenarios possible. Let’s look into the case in which  Xen is used for server consolidation: in order to apply a security update to 10 virtual servers, an administrator is required to log in into each one and run an update procedure. Since VPSs are normally indented for different users with their own projects, this is not an issue for Xen based virtualization. However, the fact that with OpenVZ a simple shell script can update all containers at once greatly eases the management of the entire system.

Conclusions

Virtualization basics as well as the main principles of two fundamentally different virtualization solutions have been described in this post. It is obvious that both projects are outstanding virtualization systems and provide host industry with sufficient number of features to support an entire type of VPS plans. Each of the engines is aimed at solving specific set of tasks, which they successfully do. Xen is a technology mainly aimed at providing the maximum approach to the full virtualization and full separation of virtual machines on the hardware carrier. It is also aimed at supporting the maximum range of existing operating systems. OpenVZ, on the other hand, is a system specifically aimed at Linux based virtual environments. It provides good dynamic resource sharing and isolation tools, which leads to higher server utilization figures. Both engines show great performance.