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Chapter 1 11
Overview
V-Class Server Architecture
Memory Interleaving
Through the memory access controllers, each memory board provides
separate read and write access to the memory DIMMs. Up to 16 DIMMs
may be installed per board, providing up to 256-way memory
interleaving per cabinet when all memory boards are fully populated.
Slots for DIMMs on each memory board are conceptually grouped in four
quadrants. Each quadrant, as Figure 8 on page 10 shows, has a separate
connection to the memory controller. All quadrants should have the same
memory configuration; this also provides good performance by
interleaving memory within a memory board.
Memory also is interleaved across memory controllers, allowing separate
controllers and separate parts of the V2500/V2600 crossbar to
simultaneously access memory on different controllers. See Figure 7 on
page 8 for details.
CTI Cache Memory
A portion of the memory on each cabinet of a V2500/V2600 SCA system
is used to implement the CTI cache memory. The CTI cache (also called
“network cache”) is memory that is used to minimize the latency of
remote memory accesses.
The CTI cache is directly mapped and physically indexed, unlike the
processor data caches. The size of the CTI cache is tunable and may
range from 8MB to 16GB, depending on the configuration of the memory
boards.
To set the CTI cache size, use the xconfig utility. The xconfig program
has a graphical interface and resides on (and is run from) the Service
Support Processor. The xconfig utility’s
Memory menu allows the CTI
cache to be set through the
Configure Network Cache menu item.
You also can configure CTI cache using the ts_config utility, which is
on the Service Support Processor. For details, see Chapter 5,
“Configuration utilities” or the ts_config man page.
The amount of memory dedicated as CTI cache must be set to be the
same for each cabinet in the V2500/V2600 server. So, for example, a
128 MByte per-cabinet CTI cache setting would consume a total of
256 Mbytes of memory for a two-cabinet V2500/V2600 server. Single-
cabinet servers should not have any memory dedicated as CTI cache, as
it is unnecessary.