Long Term Cache Hits are 0% or near 0% in MONITOR.NLM

(Last modified: 04Sep2004)

This document (10083349) is provided subject to the disclaimer at the end of this document.

fact

Novell eDirectory 8.7 for NetWare 5.1

Novell eDirectory 8.7 for NetWare 6

symptom

Long Term Cache Hits are 0% or near 0% in MONITOR.NLM which is very low.

cause

On NetWare, the caching algorithm works as follows. If something is read or written from/to disk, it stays in the cache buffer indefinitely. There is no aging process that kicks it out. The only time it will be booted is when more information is cached and the amount of free cache buffers is less the information size. When this happens, cache buffers are freed according to the oldest one first (this is the LRU Sitting Time stat). This stat tells you how fast the file system is rotating through the cache buffers and filling it up with new data from disk.  The following items need to be considered when reading this statistic:

1. This setting is only used for legacy volumes.  The long term cache hits will be zero if there are no legacy volumes. 

2. Cache Buffers are not used exclusively for filesystem cache.  Thus, if there is a legacy volume and it is rarely used, then the possibility for long term cache hits being low is also high because the cache buffers will be used and flushed for data other than the filesystem cache.  However, if the legacy volume is used consistently, then the long term cache hit % will accurately reflect the caching engine and the percentage of cache hits that occur.

3. If Direct File System calls are used, then the OS caching engine is bypassed.  The filesystem cache buffers are flushed and returned immediately to the available list, resulting in a low percentage rate.

A few things to consider with eDirectory:

1. eDirectory fits into item 3 above for most of its disk activity.  eDirectory makes Direct File System calls and does not use the file system caching engine.  The exception to this would be that eDirectory does use the file system when accessing and manipulating stream files.

2. eDirectory, by default, uses a dynamic algorithm to access as much memory as the OS will give it.  (For more information on this, see the eDirectory 8.7 Administration Guide).  A heavy eDirectory server with default settings could fit into scenario 2 above.

fix

This statistic is not valuable when evaluating a pure eDirectory server.  Use NDS iMonitor to monitor memory usage with eDirectory when dealing with file access issues.  This feature can be seen by going to http://serveraddress:port/nds/agent?config=CacheCtl.

I.E. http://10.10.10.10:8008/nds/agent?config=CacheCtl

note

The online help files in NetWare's MONITOR.NLM state that if this statistic is low, the most probable cause is that there is not sufficient memory on the server.  This statistic tracks how often the files being accessed are found in cache and do not require disk access.   In this scenario, probable cause does not apply.

fix

For additional information on eDirectory 8.7, please see the following solution.  NOVL81742  - eDirectory 8.7 Readme Addendum

document

Document Title:	Long Term Cache Hits are 0% or near 0% in MONITOR.NLM
Document ID:	10083349
Solution ID:	NOVL89625
Creation Date:	19May2003
Modified Date:	04Sep2004
Novell Product Class:	NetWare

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