IBM 990 manual Ring Topology, Memory sparing, Memory upgrades, Book replacement and memory

Draft Document for Review April 7, 2004 6:15 pm 6947ch02.fm

When activated, a logical partition can use memory resources located in any book. No matter in which book the memory resides, a logical partition has access to that memory if so allocated. Despite the book structure, the z990 is a Symmetric Multi-Processor (SMP).

Each memory card has two memory ports, and each port can access 128 bits (16 bytes). Actually, the data access path is 140 bits wide, allowing for sophisticated sparing and error-checking functions. Each port is capable of four fetch and four store operations concurrently.

Memory upgrade is concurrent when it requires no change of the physical memory card. A memory card change is disruptive.

Memory sparing

The z990 does not contain spare memory DIMMs. Instead, it has redundant memory distributed throughout its operational memory and these are 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.

Memory upgrades

For a model upgrade that results in the addition of a book, a minimum of additional memory is added to the system. Remember, the minimum physical memory size in a book is 16 GB. During a model upgrade, addition of a book is a concurrent operation. The addition of the physical memory that is in the added book is also concurrent.

If all or part of the additional memory is enabled for installation use, it becomes available to an active logical partition if this partition has reserved storage defined; see “Reserved storage” on page 70 for more detailed information. Or, it may be used by an already defined logical partition that is activated after the memory addition.

Book replacement and memory

When a book must be replaced, for example due to an unlikely MCM failure, the memory in the failing book is removed as well. Until the failing book is replaced, Power-on Reset of the CPC with the remaining books is not supported.

2.1.4 Ring Topology

Concentric loops or rings are constructed such that in a four-book system, each book only is connected to two others, which means that only data transfers or data transactions to the third book require passing through one of the other books.

Book-to-book communications are organized as shown in Figure 2-4 on page 30. Book 0 communicates with book 2 and book 3; communication to book 1 must go through another book (either book 2 or book 3).

Chapter 2. System structure and design 29