XenServer DMC (sometimes known as “dynamic memory optimization”, “memory overcommit” or “memory ballooning”) works by automatically adjusting the memory of running VMs, keeping the amount of memory allocated to each VM between specified minimum and maximum memory values, guaranteeing performance and permitting greater density of VMs per server.
Without DMC, when a server is full, starting further VMs will fail with “out of memory” errors. To reduce the existing VM memory allocation and make room for more VMs you must edit each VM’s memory allocation and then reboot the VM.
The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
Easy Way to Remember the OSI 7 Layer Model
All People Seem to Need Data Processing or Please Do Not Throw Sausage Pizza Away
A virtual machine (VM) is a software container (sometimes called a “guest”) that runs on a host physical computer and that behaves as if it were a physical computer itself. VMs consist of an operating system plus CPU, memory (RAM) and networking resources, and software applications.
A template is a virtual machine encapsulated into a file, making it possible to rapidly deploy new VMs. Each template contains installation metadata—the setup information needed to create a new VM with a specific guest operating system, and with the optimum storage, CPU, memory and virtual network configuration.
You can create new VMs and templates by copying (cloning) an existing VM or template. XenServer has two mechanisms for copying VMs and templates, full copy or fast clone:
Full copy makes a complete copy of the VM’s disks. Fast clone (Copy-on-Write) writes only modified blocks to disk, using hardware-level cloning features for copying the disks from the existing VM to the new VM. This mode is only supported for file-backed VMs.
Using xencenter, we can create our own custom templates like create a vm based on existing templates, install OS, run sysprep and shutdown, then convert to template. Using this custom template we can deploy as many vms as we need and it has some OS in it. But if we want to create an empty template(skeleton template) without any OS, we can do it by this process:
create a vm using “Other install media” template in xencenter.
To create a new storage repository, you use the New Storage Repository wizard: to open the wizard, click New Storage on the Toolbar.
Alternatively, do one of the following:
On the Storage tab for the selected pool or server, click New SR. On the Storage menu, click New SR. You select the physical storage type on the first page of the New Storage Repository wizard and then follow the steps in the wizard as it takes you through the configuration process for that storage type.
The New VM wizard takes you through the process of creating a new virtual machine (VM), step-by-step. To start the New VM wizard, on the toolbar, click New VM.
Alternatively, do one of the following:
Press Ctrl+N . On the VM menu, click New VM. Select a server in the Resources pane, right-click and then click New VM on the shortcut menu. Using the wizard, you can configure the new VM exactly the way you want it, adjusting various configuration parameters for CPU, storage and networking resources.
VMs can be imported from OVF/OVA packages, from disk images, and from XenServer XVA files. VMs can be exported as OVF/OVA packages and as XenServer XVA files. You import and export VMs in XenCenter using the Import and Export wizards. XenCenter uses the Transfer VM to transfer the content of a disk image.
When importing VMs created on hypervisors other than XenCenter, for example Hyper-V or VMware, it is necessary to use the Operating System Fixup tool to ensure that imported VMs can boot on XenServer.
Citrix XenServer is a complete, managed server virtualization platform built on the powerful Xen hypervisor. Xen technology is widely acknowledged as the fastest and most secure virtualization software in the industry. XenServer is designed for efficient management of Windows® and Linux® virtual servers and delivers cost-effective server consolidation and business continuity.
What is server virtualization? Server virtualization is a proven technology that enables multiple virtual machines to run on a single physical server.
Using XenCenter, a storage repository can be removed temporarily or permanently:
Detach. Detaching a storage repository breaks the association between the storage device and the pool or server, and its virtual disks become inaccessible. The contents of the virtual disks and the meta-information used by virtual machines to access the virtual disks are preserved. Detach can be used when you need to temporarily take a storage repository offline, for example, for maintenance.
