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Memory and I/O Configuration

This section describes how to configure memory and I/O.

Dual In-Line Memory Modules Population

For performance reasons, it is best to fully populate memory on CPU/Memory boards with the same sized Dual In-line Memory Modules (DIMMs). When a board is running with the same DIMM type in each bank, DIMM performance is maximized. The Sun Fire 15K server supports a maximum of 288 gigabytes of physical memory using 512 megabyte DIMMs and 576 gigabytes of physical memory, using 1-gigabyte DIMMs. The maximum physical memory supported per domain is 576 gigabytes with Solaris 8 OS (02/02) and 288 gigabytes with Solaris 8 OS (10/01).


Always fully populate memory with the same-sized DIMMs.


Physical addresses on the CPU/Memory board are interleaved across the four memory controllers, where each controller has four logical banks. The defaults are an 8-way interleave for a half-populated board and a 16-way interleave for a fully populated board. To disconnect via DR a CPU/Memory board, interleaving has to be set within the board. The interleaving setting is verified with the prtdiag command. While other interleave values could be applied, they are not recommended.


For DR purposes, interleaving across boards is not recommended. Use interleaving within the CPU/Memory board.

Page Scanning on Large Memory Systems

In most circumstances, systems are configured with sufficient physical memory such that little or no swapping or paging is required to manage page allocation. The two parameters affecting page allocation are fastscan and handspreadpages. It is recommended that the values for these parameters be set as shown in the following examples. Review the Solaris Tunable Parameters Reference Manual for a full description of these parameters.

set fastscan=65536
set handspreadpages=physmem/4


Tune these variables as suggested.

File System Flush

Two parameters affect the Solaris OS file system flush daemon. Review the Solaris Tunable Parameters Reference Manual for a full description of these parameters. The file system flush daemon searches for and flushes dirty file system pages.

By default, the daemon wakes up every five seconds and scans 1/6th of the physical memory, thus flushing all physical memory within 30 seconds. On large memory systems, the daemon consumes a large amount of CPU if there are many file system pages in the file system page cache. In some circumstances, the daemon is not able to complete its scan of 1/6th of the physical memory at each scheduled wake up. Revised parameters correct this behavior; a larger value for the autoup parameter is recommended. Increasing the default from 30 seconds to (nGB x 4) is recommended. For example, a system configured with 96 gigabytes of memory should have an autoup value of 384 (96x4). The autoup parameter can be revised in file /etc/system.


Set autoup= nGB x 4. (Example: 384 for 96 gigabytes of memory.)

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