The terms FMA and IMA are synonomous with Citrix and the technologies offered and understanding what these terms means is important. As legacy and current use of technology has implication in how these terms are used.
FMA is the current management architecture used by Citrix software like XenApp and XenDesktop and this is stands for the FlexCast Management Architecture, FMA for short. FMA replaced the older Independent Management Architecture (IMA) architecture used on XenApp 6.5 and older versions including XenApp 5.0, Presentation Server and MetaFrame.
FMA was introduced originally in XenDesktop version 5.0 (for VDI) and for XenApp as XenDesktop 7 App Edition and now has become the mainstay of all products in the VDI space developed by Citrix.
The IMA architecture used by older versions of XenApp had a different database architecture and used different design concepts to later XenApp and XenDesktop versions.
Independent Management Architecture (IMA) used a central database known as a IMA Data Store (often described as a database within a database) to store persistent configuration information. The IMA Data Store could be stored on Microsoft SQL, Microsoft Access or Oracle databases.
The boundary concept for IMA was the ‘Farm’ which can be further partitioned into Zones with a ‘Most Preferred’ Zone Data Collector responsible for maintaining dynamic ‘in-memory’ information from server loads, session statuses, published applications/desktops details, users connected to license usage.
The Zone Data Collector pulled persistent configuration information about the XenApp Farm from the IMA Data Store and used this along with its dynamic information to make decisions about which Citrix XenApp server to direct users to when users launch published applications and desktops.
Local Host Cache
Each XenApp server maintained a copy of the persistent information in the IMA Data Store pertinent to itself known as the Local Host Cache (LHC). The XenApp servers updated their LHC every thirty minutes. The LHC was a local Microsoft Access database and is used by XenApp 6.5 farms (including XenApp 6.0, XenApp 5.0, Presentation Server and MetaFrame).
When the IMA Data Store wasn’t available, the XenApp servers provided information stored in their Local Host Cache (LHC) to the Data Controllers, to facilitate the connection decisions the Zone Data Collector makes. During this period Administrators were unable to make changes to the Citrix Farm configuration.
The FMA Architecture used by later versions of XenApp and XenDesktop was fundamentally different to IMA and several iterations of FMA brought additional functionality, which in many cases was provided by IMA.
FlexCast Management Architecture (FMA) uses a central database on Microsoft SQL server to store persistent configuration information such as the configuration of the XenApp site.
The boundary concept for FMA is the ‘Site’, Controllers responsible for maintaining dynamic ‘in-memory’ information from server loads, session statuses, published applications/desktops details, users connected to license usage.
The Controllers pull information from the FMA database and uses this along with its dynamic information to direct access to the correct XenApp servers. When the FMA database isn’t available, the Connection Leasing is used.
Connection Leasing allows users to still be able to connect to their recent applications and desktops (from previous two week period) when the database is not available. Pooled non-persistent desktops are not protected by connection leasing.
Each Site Controller caches user connection details of the applications and desktops they are connected to. The Controllers retain a cache of two weeks’ worth of connection details for each user who has connected within that period. Anything longer is purged.
The benefits of Connection Leasing only come to light when the SQL database is not available, the Controllers enter ‘leased connection mode’ allowing users to still connect to applications and desktops they have used recently used from the cache details held by the Controllers. When the Controllers are in ‘lease connection mode’ the Site Administrators are unable to make Site configuration changes.