IBM 990 - Manual (Page 79)

Chapter 2. System structure and design 67
with operator controls for its associated CPC, so you can target operations in parallel to
multiple or all CPCs, or to a single CPC.
The second SE, called Alternate SE, is standard on all z990 models and serves as a backup
to the primary SE. Error detection and automatic switch-over between the two redundant SEs
provides enhanced reliability and availability. There are also two fully redundant interfaces,
known as the Power Service Control Network (PSCN), between the two SEs and the CPC.
For further information on the Hardware Management Console and SEs, refer to Appendix A,
“Hardware Management Console (HMC)” on page 235.
Dual External Time Reference
The z990 implements a dual External Time Reference (ETR). The optional ETR cards
provide the interface to the IBM Sysplex Timers, which are used for timing synchronization
between systems in a Sysplex environment.
If z990 models have coupling links, then two ETR cards with dual paths to each book are
installed, allowing continued operation even if a single ETR card fails. This redundant design
also allows concurrent maintenance.
2.2.8 Storage operations
In z990 servers, memory can be assigned as a combination of central storage and expanded
storage, supporting up to 30 logical partitions.
Before you activate a logical partition, central storage (and optional expanded storage) must
be defined to the logical partition. All installed storage can be configured as central storage.
Each individual logical partition can be defined with a maximum of 128 GB of central storage.
Central storage can be dynamically assigned to expanded storage and back to central
storage as needed, without a Power-on Reset (POR) (refer to “LPAR single storage pool” on
page 55 for further details).
Memory cannot be shared between system images. You can dynamically reallocate storage
resources for z/Architecture and ESA/390 Architecture mode logical partitions running
operating systems that support Dynamic Storage Reconfiguration (DSR) (refer to 2.2.11,
“LPAR Dynamic Storage Reconfiguration (DSR)” on page 71 for further details).
Operating systems running under z/VM can exploit the z/VM capability of implementing virtual
memory to guest virtual machines. The z/VM dedicated
real storage can be “shared” between
guest operating systems’ memories.
Note: The z990 (and the z890) are the last zSeries servers offering Token Ring adapters
on the Hardware Management Consoles and Support Elements. Timely planning is
advised in preparation of migration to the Ethernet environment.
Note: Hardware Management Consoles are to become closed platforms with the next
zSeries server and will only support the HMC application. Other applications, such as for
the IBM ESCON Director and the IBM Sysplex Timer, will no longer be supported from the
HMC. Timely planning for needed console equipment for Directors and Timers is
recommended. When available, these HMCs can only communicate with Generation 5
servers and later (Multiprise® 3000, G5, G6, z800, z900, z890, z990) and TCP/IP will be
the only communication protocol supported.