User Guide

Understanding Server Memory 11
Server Memory Administration Guide
103-000147-001
August 30, 2001
Novell Confidential
Manual 99a38 July 17, 2001
also tune the number of directory cache buffers yourself, using two server
parameters that establish the minimum and maximum number of directory
cache buffers the server can allocate. For information about tuning directory
cache, see “Tuning Directory Cache for the Traditional File System” on page
24.
File cache is used with both the traditional file system and the NSS file system.
File cache is a pool of 4 KB memory pages. File cache stores recently used file
data and also parts of the Novell eDirectory
TM
database.
In an ideal environment, there is enough memory so that all frequently used
data can be retrieved from file cache rather than from disk.
Monitoring the disk cache utilization statistic can help you estimate whether
your server has sufficient memory to service requests from cache. For
information about optimizing file cache, see “Tuning File Cache” on page 20.
Logical Memory Addressing
The physical memory of the server is divided into 4 KB blocks, called pages.
When a NLM program wants to store information in memory, it requests
memory pages that are contiguous, so that all the information can be stored in
a sequential group of pages.
As contiguous blocks of memory pages are allocated and then made free,
small segments of memory are often left over. After a while, there are many
such isolated pieces of memory too small to be used. This situation is called
memory fragmentation. When memory is fragmented, the server often cannot
satisfy memory requests even when a lot of memory is available.
NetWare's logical memory addressing scheme helps to prevent memory
fragmentation. The memory management subsystem provides a logical space
manager that lists logical memory addresses from 0 to 4 GB. The logical space
manager lists addresses up to 4 GB even if the server contains only the
minimum 256 MB of RAM.
When an NLM program needs a contiguous block of memory, the operating
system finds a set of logical, contiguous addresses in the logical space.
Because table has so many logical addresses (4 GB), the operating system can
almost always find the contiguous logical memory addresses the NLM
program needs. Then the operating system allocates physical memory which
might or might not be contiguous. The operating system then binds the logical
addresses to the physical addresses.