Virtualization offers a number of advantages over "classic" server operation:
In addition to use for its own services, BITS also provides capacity for use of this technology by faculties and departments. This offer, called "vHosting", offers similar conditions as the already known "Server Housing"
,except that the customer does not have to provide his own hardware.
Virtualization technology is now so advanced that there are hardly any applications that are unsuitable for virtualization. However, the principle of "a lot helps a lot" applies. Appropriate resources must be available for efficient virtualization of demanding systems, i.e. many fast CPUs, sufficient main memory, fast networks and plenty of fast hard disk storage.
The resources provided as part of the vHosting cluster are limited, so not just any use cases can be implemented in them (see Hardware). High-power computing or terabyte-sized databases cannot currently be mapped. But many other use cases can be easily implemented with this platform:
Especially the possibility to create snapshots of a virtual machine is an enormous advantage for test and development systems compared to physical systems.
Before ordering a virtual machine, the requirements and expectations should be discussed with BITS.
Virtualization is a strategic platform for the operation of central services at BITS. Therefore, the underlying systems are designed to guarantee uninterrupted operation even if large parts of the infrastructure should fail. These standards also underlie the vHosting cluster.
The vHosting cluster is currently based on the following systems:
The connections to the network and storage systems are redundant. The servers are distributed across the two BITS data center locations, and the storage is provided synchronized at both locations. This configuration means that even the failure of a complete location does not lead to a failure of the vHosting cluster.
Currently, 8 terabytes of hard disk space are available in the storage system for the vHosting cluster. In addition, there is sufficient NAS storage to provide daily backups of all virtual machines for one to two weeks.
These backups are based on snapshots of the virtual machines. This means that restored virtual machines cannot be guaranteed to have a fully consistent file system, they are only "crash consistent". Modern file systems , which use Utilities Control Room such as journaling, can usually repair such restored file systems. For critical data with a high rate of change (e.g. databases), an additional backup is recommended, ideally via TSM.
One advantage of a virtual machine over a physical system is the ability to take snapshots. A snapshot captures and freezes the overall state of a virtual machine. This includes the main memory, the CPU and the virtualized hard disks. After a snapshot has been created, the virtual machine continues to run, and the creation of the snapshot itself can be done without interrupting operation. Afterwards, it is possible to jump back to the state at which the snapshot was created at any time. A snapshot is therefore excellent for protecting critical changes to the virtual machine. These can be updates to the operating system or software, configuration changes or other tests.
Snapshots require additional resources and restrict some functions of the virtualization environment. Snapshots are therefore intended to have a short lifetime (a few days at most) and are not suitable for keeping a particular state for a longer period of time. In particular, they are not a substitute for a backup.
Further information on the side effects of snapshots can be found in the following VMware knowledge base article:
Rule of the game: Snapshots should be removed after a few days at the latest.
The VMware Tools are a piece of software that is installed in the guest operating system of a virtual machine. Besides some facilitations for the user (better usable console), the VMware Tools allow the virtualization software (the hypervisor) to influence the guest operating system. This is particularly necessary when the physical main memory becomes scarce. With the help of VMware Tools, the hypervisor can better control the memory consumption of the virtual machines. Without VMware Tools, significantly greater performance losses for the virtual machine are the result in this case.
VMware Tools can be installed using the vSphere Client. Detailed instructions can be found in VMware knowledge base articles:
The correct installation of VMware Tools is displayed in the "Overview" tab.
Game rule: The VMware tools must be installed and kept up to date.
Bielefeld University departments and faculties can purchase virtual machines on the vHosting cluster. The annual rent for a virtual server is currently 100 euros. All virtual machines are backed up nightly; these backups are available on request for between one and two weeks.
When scaling the virtual hardware (number of CPUs, main memory, hard disk space), a sense of proportion should be used, as several virtual machines share the actual hardware available. Many hardware requirements of standard software are based on dedicated physical systems, which are dimensioned too large rather than too small in order to avoid migration to a higher expansion level in the event of resource bottlenecks. Virtualization allows much more precise scaling of virtualized hardware, which can be easily expanded as needed.
The following information must be specified when ordering a virtual machine:
When scaling the virtual hardware (number of CPUs, main memory, hard disk space), a sense of proportion should be used as several virtual machines share the hardware that is actually available. Many hardware requirements of standard software are based on dedicated physical systems, which are dimensioned too large rather than too small in order to avoid migration to a higher expansion level in the event of resource bottlenecks. Virtualization allows much more precise scaling of virtualized hardware, which can be easily expanded as needed.
The following information must be specified when ordering a virtual machine:
|Name||The virtual machine is identified within the vSphere cluster by a name. This should allow the virtual machine to be identified easily and without doubt so that no misunderstandings arise in the event of queries and fault processing. This name does not have to be identical to the name of the machine in the DNS, Active Directory or other directory system, but here too a uniform name prevents misunderstandings and confusion.|
|Operating system||VMware supports a number of operating systems(see VMware's compatibility list), other operating systems for x86/amd64 processors usually work as well, but are not officially supported. Templates exist for Windows Server, other operating systems currently have to be installed by the user.|
|Number of CPUs||The department of multi-processor systems takes place only in justified exceptional cases, or if the need could be determined by longer operation. As a rule, virtual machines are initially set up with one virtual processor.|
|Main memory||The main memory should be adapted to the actual application. Various operating systems and applications (databases, Java) tend to occupy all available memory and thus give the impression of permanent memory shortage. However, more precise analyses then show that only a fraction of this memory is actually used. As a rule, the virtual machine should get by with 1 to 2 GBytes of main memory. An extension can be made if the need has actually been proven in operation.|
|Hard disk space||Current operating systems should get by with 10 to 40 GBytes of hard disk space. About the same amount can be provided for data. Fully virtualized operation of systems with very large amounts of data is currently not possible with the available resources. If required, large data volumes must be stored outside the virtual machine and integrated via NFS/CIFS. See the BITS documentation for more information.|
|Supervisor/Owner||For the installation and administration of the virtual machines via the vCenter Server, a user ID in the Active Directory of Bielefeld University (domain "AD") is required. Between 1 and 3 staff, people can have administrative rights to a virtual machine.|
Currently, all virtual machines of the vHosting cluster are operated in the same network as the physical machines in the housing area. IP addresses are assigned via DHCP, but static addresses can be department if required.
Ordering a virtual machine is done by providing all the above information via email@example.com.
Virtualization means that several virtual machines share the same physical hardware. To ensure that the available resources can be shared fairly among all users, some rules of the game must be observed.
To be able to quickly contact the owner of a virtual machine in case of queries, an e-mail address must be stored. To do this, select "Edit" in the "Notes" field in the overview tab of the vSphere Client and enter an e-mail address in the dialog that appears under "maintainer_email".
If required, multiple addresses can be entered, separated by commas. However, it is recommended to enter a role address instead, which can be used to contact several staff, people if required. A mailing list is created from the e-mail addresses stored in this way, which is used to inform the virtual machine owners about changes and failures of the vHosting cluster.
Rule of the game: A meaningful contact address must be stored in the vSphere Client.