Chapter 2 HPSS PlanningHPSS Installation Guide September 2002 81Release 4.5, Revision 2must be in use before purging begins, and a lower bound specifying the target percentage of freespace to reach before purging is stopped.2.6.17 Non-DCE Client GatewayThe Non-DCE Client Gateway provides HPSS access to applications running without DCE and/orEncina which make calls to the Non-DCE Client API. It does this by calling the appropriate ClientAPIs itself and returning the results to the client. Any system which wishes to make use of the Non-DCE Client APIs must have a properly configured and running NDCG.An HPSS installation can have multiple NDCG servers. A client can utilize a particular NDCGserver by setting its HPSS_NDCG_SERVERS environment variable with the hostname and portof the target NDCG server.The NDCG can be configured to support client authentication. A single NDCG can be configuredto support Kerberos and/or DCE authentication. The client requests one of the supportedauthentication methods during the initial connection. Client authentication can also be completelydisabled on a NDCG server basis. In this case, the NDCG server believes the identity of the clientsent during the initial connection. When using DCE authentication, the DCE identity and passwordare passed in an encrypted format from client to server during the initial connection. The NDCGcan be configured to support either DES or simple hashing function for encryption of the DCEidentity and password that is passed to the NDCG.See Section 2.3.4.2: HPSS Non-DCE Mover/Client Machine on page 51 for more information onprerequisites for a Non-DCE configuration.2.7 Storage Subsystem ConsiderationsStorage subsystems have been introduced into HPSS for the purpose of increasing the scalability ofthe system - particularly with respect to the name and bitfile servers. In releases prior to 4.2, anHPSS system could only contain a single name and bitfile server. With the addition of storagesubsystems, an HPSS system must now contain one or more storage subsystems, and each storagesubsystem contains its own name and bitfile servers. If multiple name and bitfile servers aredesired, this is now possible by configuring an HPSS system with multiple storage subsystems.A basic HPSS system contains a single storage subsystem. Additional storage subsystems allow theuse of multiple name and bitfile servers, but also introduce additional complexity in the form ofextra subsystems and servers being defined. Storage subsystems can also be used to increasescalability with respect to SFS, but the price of this is that each storage subsystem requires its owncopies of several metadata files to support the servers in that subsystem. Finally, storagesubsystems provide a useful way to partition an HPSS system, though they also require that storageresources be fragmented in order to support the multiple subsystems.2.8 Storage Policy ConsiderationsThis section describes the various policies that control the operation of the HPSS system.
