In server environments that are virtualized with Citrix XenServer, you can connect the server to the SAN by putting a host bus adapter or iSCSI initiator in the XenServer host and have that present the LUNs on the SAN. That method works fine, but there’s another, more integrated option, using StorageLink from Citrix.
Without Citrix StorageLink, all storage arrays look the same to the XenServer host no matter what SAN you’re using. With StorageLink, the SAN is integrated within your Citrix environment. That means that from within the StorageLink Manager interface (found on the Windows server’s Start menu), you get access to advanced features that are offered by the storage array -- such as cloning, deduplication and creating snapshots -- which makes managing storage easier.
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In addition, for supported storage arrays, at the beginning of the storage management lifecycle, Citrix StorageLink is able to automatically detect either iSCSI or Fibre Channel storage connections for immediate use. This is particularly beneficial for environments where multiple storage arrays are used, since setting up storage without StorageLink involves a lot of work and knowledge of each array. StorageLink eliminates the need to have in-depth knowledge of all arrays. This means that the task of managing storage can be shifted from the storage administrator to the administrator of the virtual environment.
Another benefit is that StorageLink offloads storage operations from the hypervisor to the storage array. Without StorageLink, storage-related tasks are initiated from the virtual environment, which has to wait for the storage array to complete the operation. Only once the completion is confirmed can the virtual environment continue. With StorageLink, the operation is performed by the storage array, taking just seconds of time on the part of StorageLink Manager. The StorageLink interface simply displays the result of the work processed at the storage array.
The final benefit is that with Citrix StorageLink, the process of setting up virtual machines is much easier. That’s because StorageLink enables you to create virtual machines from templates and configure storage directly from templates, even in environments where storage arrays from different vendors are used side by side. Administrators set up hardware or storage profiles for VMs and link them directly to the LUNs on the storage array, with access to the array’s snapshot and cloning functionality.
StorageLink requirements and components
To use StorageLink, you need the Enterprise or Platinum version of Citrix Essentials for XenServer, a management layer that runs on top of XenServer.
StorageLink comprises two components. The core component is StorageLink gateway, a server (which can run as a VM) that connects to the virtualization hosts and to the storage arrays and runs a database in which the host information is stored. This gateway runs on Windows Server 2003 Release 2 or higher. The second component is the aforementioned StorageLink Manager, which provides three interfaces for managing storage: a graphical user interface, a PowerShell interface and a command line interface.
Do you need StorageLink?
Citrix StorageLink is an optional product. You can perfectly manage your Citrix XenServer environment without it. In larger environments, with hundreds of virtual servers or desktops, where dynamic management of storage is a requirement, StorageLink is a valuable addition since it enables you to automate the deployment of virtual machines. If you’re running just a few virtual servers, you don’t need it; you might as well set up storage manually to avoid the cost of StorageLink.
Sander van Vugt is an independent trainer and consultant based in the Netherlands.