Chapter 2. System structure and design 53
Draft Document for Review April 7, 2004 6:15 pm 6947ch02.fm
Table 2-3 PU chip allocation
򐂰On a single-book configuration, model A08:
– When a PU failure occurs on a dual-core chip, the two standard spares PUs are used
to recover the failing chip, even though only one of the PUs has failed.
– When a failure occurs on a PU on a single-core chip, one standard spare PU is used.
The system does not issue an RSF call in either of the above circumstances.
When a non-characterized PU is used as a spare, in case the system has run out of the
standard spares, or when all PUs have been assigned and no non-characterized PU
remains available, an RSF call occurs to request a book repair.
򐂰On a multi-book configuration, models B16, C24, or D32
– In a first step, the standard spare PUs of the MCM where the failing PU resides is
assigned as spare, in the same manner as for a one-book system.
– In a second step, when there are not enough spares in the book with the failing PU,
non-characterized PUs in other books are used for sparing. When “cross-book” sparing
occurs, the book closest to the one with the failing PU will be used.
For example, if a PU failure in Book-1 cannot be solved within locally, spares in Book-2
or Book-0 are then selected. When no spares are available in any adjacent book,
Book-3 is approached for a spare PU.
2.2.5 Memory design
As for PUs and the I/O subsystem designs, the z990 memory design equally provides great
flexibility and high availability, allowing:
򐂰Concurrent Memory upgrades, except when the physically installed capacity is reached.
The z990 servers may have more physically installed memory than the initial available
capacity. Memory upgrades within the physically installed capacity can be done
concurrently by the Licensed Internal Code, and no hardware changes are required.
Concurrent memory upgrades can be done via Capacity Upgrade on Demand or
Customer Initiated Upgrade. Note that memory upgrades cannot be done via Capacity
BackUp (CBU); see Table8-1 on page 188 for more information.
򐂰Dynamic Memory sparing
The z990 does not contain spare memory DIMMs. Instead, it has redundant memory
distributed throughout its operational memory and this is used to bypass failing memory.
Replacing memory cards requires the removal of a book and this is disruptive. The
extensive use of redundant elements in the operational memory greatly minimizes the
possibility of a failure that requires memory card replacement.
Core Core X = CP, IFL, ICF, or zAAP
Single
core 0- X -
2- X -
4- X -
6- X -
Dual
core 89 X Spare
AB X Spare
C D X SAP
E F X SAP