Access groups provide a means to arrange and restrict access to storage to a limited set of servers. In Oracle VM there are two types of access groups that ultimately provide very similar functionality:
File System Access Groups define which Oracle VM Servers have access to a particular file server export or file system. This is commonly used in environments where a file server has non-uniform exports, since it is important to be able to determine which Oracle VM Servers are able to refresh the file system. This is discussed in more detail in Section 3.6, “What are Uniform and Non-uniform Exports?”.
SAN Access Groups define which storage initiators can be used to access physical disks exposed using some form of SAN storage, such as iSCSI or Fibre Channel. SAN access group functionality is defined by the Oracle VM Storage Connect plug-in that you are using. The generic iSCSI plug-in creates a single access group to which all available storage initiators are added at the time of discovery. Other plug-ins provide more granular control allowing you to create multiple access groups that limit access to particular physical disks according to your requirements.
It is possible that in some environments you may have mixed SAN storage, where both iSCSI and Fibre Channel types are available. This can cause some confusion when configuring access groups, since the storage initiators for an access group must match the type of storage that the access group is being configured for. Oracle VM Manager is unable to filter the storage initiators available on each Oracle VM Server according to type, since access group contents are defined by the Oracle VM Storage Connect plug-in manufacturer. Therefore, it is important to pay attention to the storage initiators that you add to an access group if you are in an environment that supports more than one storage type. In most cases, creating an access group that contains storage initiators of a different type to that of the storage array type causes the Oracle VM Storage Connect plug-in to generate an error.