Core Server - IBM High Performance Storage System HPSS Installation Manual

3.7.1. Core Server

The Core Server is responsible for managing the HPSS name space (files, directories, links, etc.),
bitfiles, and storage (physical volumes, virtual volumes, etc.) for a single subsystem. Each of these
areas of responsibility are outlined in greater detail below.
Core Server at large
The Core Server uses POSIX threads to service concurrent requests. The Core Server accepts
requests from any authenticated client; however, certain Core Server functions can be performed only
by trusted clients. Trusted clients are those for whom control permission has been set in the Core
Server's ACL entry for the client. Higher levels of trust are granted to clients who have both control
and write permission set in their ACL entry. Refer to Section 2.1: HPSS Server Security ACLs of the
HPSS Management Guide for information concerning the ACL for the Core Server.
The Core Server can be configured to allow or disallow super-user privileges (root access). When the
Core Server is configured to allow root access, the UID of the super-user is configurable.
HPSS systems configured with multiple subsystems employ multiple Core Servers and multiple
metadata databases. Though the servers are separate, each Core Server in a given HPSS realm must
share the fileset global metadata table.
Name Space
The HPSS Core Server maintains the HPSS name space in system metadata. Refer to Section 3.5:
HPSS Sizing Considerations on page 68 for details on sizing the name space. Refer to Section 14.8:
DB2 Space Shortage of the HPSS Management Guide for information on handling a metadata space
shortage. By utilizing multiple storage subsystems, it is possible to distribute large name spaces
across multiple Core Servers. Junctions between the names spaces of these storage subsystems can be
used to "join" these subsystems.
Bitfiles
The Core Server provides a view of HPSS as a collection of files. It provides access to these files and
maps the files onto underlying storage objects.
When a Core Server is configured, it is assigned a server ID. This value should never be changed
because it is embedded in the ID of each bitfile and storage segments it uses. HPSS expects to be able
to extract the Server ID from any bitfile ID and connect to that server to access the file.
The Core Server maps bitfiles to their underlying physical storage by maintaining information that
maps a bitfile to the storage segments that contain its data. For additional information, see Section
3.7.1: Core Server on page 81. The relationship of bitfiles to storage segments and other structures is
shown in Figure 9: The Relationship of Various Server Data Structures.
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 81