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Chapter 2 HPSS Planning
64 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
2.6.3 Disk Storage Server
Each Disk Storage Server manages random access magnetic disk storage units for HPSS. It maps
each disk storage unit onto an HPSS disk Physical Volume (PV) and records configuration data for
the PV. Groups of one or more PVs (disk stripe groups) are managed by the server as disk Virtual
Volumes (VVs). The server also maintains a storage map for each VV that describes which portions
of the VV are in use and which are free. Figure 2-1 shows the relationship of SS data structures such
as VVs to other server data structures.
Each Disk Storage Server must have its own set of metadata files (storage map, storage segment,
VV, and PV) in SFS. Disk Storage Servers may not share metadata files among themselves.
Once a Disk Storage Server is established in the system and a server ID is selected, the server ID
must never be changed. The BFS uses the server ID, which can be found inside storage segmentIDs,
to identify which Disk Storage Server provides service for any given disk storage segment. If the
server ID is changed, disk storage segments provided by that server will be unreachable. A Disk
Storage Server ID can be changed only if all of the server’s storage segments have been removed
from the system.
The server can manage information for any number of disk PVs and VVs; however, because a copy
of all of the PV, VV, and storage map information is kept in memory at all times while the server
runs, the size of the server will be proportional to the number of disks it manages.
The Disk Storage Server is designed to scale up its ability to manage disks as the number of disks
increases. As long as sufficient memory and CPU capacity exist, threads can be added to the server
to increase its throughput. Additional StorageSubsystems can also be added to asystem, increasing
concurrency even further.
2.6.4 Tape Storage Server
Each Tape Storage Server manages serial access magnetic tape storage units for HPSS. The server
maps each tape storage unit onto an HPSS tape PV and records configuration data for the PV.
Groups of one or more PVs (tape stripe groups) are managed by the server as tape VVs. The server
maintains a storage map for each VV that describes how much of each tape VV has been written
and which storage segment, if any, is currently writable in the VV. Figure 2-1 shows the relationship
of SS data structures such as VVs to other server data structures.
Each Tape Storage Server must have its own set of metadata files (storage map, storage segment,
VV, and PV) in SFS. Tape Storage Servers may not share metadata files among themselves.
Once a Tape Storage Server is established in the system and a server ID is selected, the server ID
must never be changed. The BFS uses the server ID, which can be found inside storage segmentIDs,
to identify which Tape Storage Server provides service for any given tape storage segment. If the
server ID is changed, tape storage segments provided by that server will be unreachable. A Tape
Storage Server ID can be changed if all of the server’s storage segments have been removed from
the system, but this is a time-consuming task because it requires migrating all the server’s tape
segments to another Storage Server.
The server can manage information for any number of tape PVs and VVs. The Tape Storage Server
can manage an unlimited number of tape PVs, VVs, maps, and segments without impacting its size
in memory.