XenServer 6.5 sees the retirement of the Integrated StorageLink Feature, which is line with deprecation notice given in XenServer 6.2 and detailed in the XenServer 6.5 release notes
With XenServer 6.2 Citrix announced that Integrated StorageLink (iSL) is a deprecated feature (development stopped on it and removal in a future release).

Background: XenServer 6 introduced Integrated StorageLink Capabilities. It replaces the StorageLink Gateway technology used in previous editions and removes the requirement
to run a VM with the StorageLink components. It provides access to use existing storage array-based features such as data replication, de-duplication, snapshot and
cloning. Citrix StorageLink allows to integrate with existing storage systems, gives a common user interface across vendors and talks the language of the storage array i.e. exposes the native feature set in the storage array. StorageLink also provides a set of open APIs that link XenServer and Hyper-V environments to third party backup solutions and enterprise management frameworks. There is a limited HCL for StorageLink supporting arrays. Details: http://bit.ly/1xS2J0m