System Administration Guide: Devices and File Systems

Collecting CacheFS Statistics

Collecting CacheFS statistics enables you to do the following:

Determine an appropriate cache size.
Observe the performance of the cache.

These statistics help you determine the trade-off between your cache size and the desired performance of the cache.

The following table describes the CacheFS statistics commands.

Command	Description	Man Page
`cachefslog`	Specifies the location of the log file. This command also displays where the statistics are currently being logged, and enables you to stop logging.	cachefslog(1M)
`cachefswssize`	Interprets the log file to give a recommended cache size.	cachefswssize(1M)
`cachefsstat`	Displays statistical information about a specific CacheFS file system or all CacheFS file systems. The information provided in the command output is taken directly from the cache.	cachefsstat(1M)

Note –

You can issue the CacheFS statistics commands from any directory. You must be superuser to issue the cachefswssize command.

The CacheFS statistics begin accumulating when you create the log file. When the work session is over, stop the logging by using the cachefslog -h command, as described in How to Stop CacheFS Logging.

Before using the CacheFS statistics commands, you must do the following:

Set up your cache by using the cfsadmin command.
Decide on an appropriate length of time to allow statistical information to collect in the log file you create. The length of time should equal a typical work session. For example, a day, a week, or a month.
Select a location or path for the log file. Ensure that sufficient space to allows for the growth of the log file. The longer you intend to allow statistical information to collect in the log file, the more space you need.

Note –

The following procedures are presented in a recommended order. This order is not required.

How to Set Up CacheFS Logging

Set up logging.
$ cachefslog -f log-file-path /mount-point
-f

Sets up logging.

log-file-path

Specifies the location of the log file. The log file is a standard file you create with an editor, such as vi.

/mount-point

Designates the mount point (CacheFS file system) for which statistics are being collected.

Verify that you correctly set up the log file.
$ cachefslog /mount-point

Example 19–13 Setting Up CacheFS Logging

The following example shows how to set up the /var/tmp/samlog log file to collect statistics about the /home/sam directory.

$ cachefslog -f /var/tmp/samlog /home/sam
  /var/tmp/samlog: /home/sam

How to Locate the CacheFS Log File

Display where CacheFS statistics are being logged.
$ cachefslog /mount-point
where /mount-point specifies the CacheFS file system for which you want to view the statistics.

You can also use the cachefslog command with no options to locate a log file for a particular mount point.

Example 19–14 Locating the CacheFS Log File

The following example shows what you would see if a log file has been set up. The location of the log file is /var/tmp/stufflog.

$ cachefslog /home/stuff
	 /var/tmp/stufflog: /home/stuff

The following example shows that no log file has been set up for the specified file system.

$ cachefslog /home/zap
	not logged: /home/zap

How to Stop CacheFS Logging

Use the cachefslog -h option to stop logging.

$ cachefslog -h /mount-point

The following example shows how to stop logging on /home/stuff.

$ cachefslog -h /home/stuff
not logged: /home/stuff

If you get a system response other than the response specified here, you did not successfully stop logging. Determine if you are using the correct log file name and mount point.

How to View the Working Set (Cache) Size

You might want to check if you need to increase the size of the cache. Or, you might want to determine the ideal cache size based on your activity since you last used the cachefslog command for a particular mount point.

Become superuser on the client system.

View the current cache size and highest logged cache size.
# cachefswssize log-file-path
For more information, see cachefswssize(1M).

Example 19–15 Viewing the Working Set (Cache) Size

In the following example, the end size is the size of the cache at the time you issued the cachefswssize command. The high water size is the largest size of the cache during the timeframe in which logging occurred.

# cachefswssize /var/tmp/samlog
 
    /home/sam
	       end size:  10688k
	high water size:  10704k
 
    /
	       end size:   1736k
	high water size:   1736k
 
    /opt
	       end size:    128k
	high water size:    128k
 
    /nfs/saturn.dist
	       end size:   1472k
	high water size:   1472k
 
    /data/abc
	       end size:   7168k
	high water size:   7168k
 
    /nfs/venus.svr4
	       end size:   4688k
	high water size:   5000k
 
    /data
	       end size:   4992k
	high water size:   4992k
 
    total for cache
	   initial size: 110960k
	       end size:  30872k
	high water size:  30872k

Viewing CacheFS Statistics

The following table explains the terminology that is displayed in the statistics output for CacheFS file systems.

Table 19–2 CacheFS Statistics Terminology


Output Term	Description
`cache hit rate`	The rate of cache hits compared to cache misses, followed by the actual number of hits and misses. A cache hit occurs when the user wants to perform an operation on a file or files, and the file or files are actually in the cache. A cache miss occurs when the file is not in the cache. The load on the server is the sum of cache misses, consistency checks, and modifications (modifies).
`consistency checks`	The number of consistency checks performed, followed by the number that passed, and the number that failed.
`modifies`	The number of modify operations. For example, writes or creates.

How to View CacheFS Statistics

View the statistics with the cachefsstat command. You can view the statistics at any time. For example, you do not have to set up logging in order to view the statistics.

View CacheFS statistics.
$ cachefsstat /mount-point
where /mount-point specifies the CacheFS file system for which you want to view the statistics.

If you do not specify the mount point, statistics for all mounted CacheFS file systems will be displayed.

Example 19–16 Viewing CacheFS Statistics

This example shows how to view statistics on the cached file system, /home/sam.

$ cachefsstat /home/sam
	    cache hit rate: 73% (1234 hits, 450 misses)
	consistency checks: 700 (650 pass, 50 fail)
	          modifies: 321
garbage collection:  0