SAR -b interpretation Post: 87617

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Top Forums UNIX for Advanced & Expert Users SAR -b interpretation Post 87617 by jim mcnamara on Wednesday 26th of October 2005 10:12:04 AM

10-26-2005

Registered User

Actually - what are you doing?

Unless you really have I/O problems - or disk thrashing - or some clearly defined problem, like every process is totally I/O bound, you should probably leave things alone.

It appears to me like you do not know what you are looking at, so your changing things could lead to big trouble.

Process space can also have file caches or buffers. Applications control caching (buffering) and that's where control of buffers usually should start, not at the kernel level. Look for applications that have called setvbuf() to turn off buffering, for example.

In general, disks have pretty big on-board caches, so you don't have to worry too much about the kernel cache if things are working reasonably well.

The write thing is the number of cache hits/misses - misses caused by writing new data to files; hits are a write updating an existing record in the cache, like a row in a database table.

Generally, the best thing to do is called load-leveling - placing really active directories on physically separate disks. This mostly applies to writes, but if there are lots of reports running you may also have a problem with reads bombing one disk, so move directories around in that case as well. The I/O request queue indicates the magnitude of this problem.

jim mcnamara

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cachefsstat

cachefsstat(1M) 					  System Administration Commands					   cachefsstat(1M)

NAME

       cachefsstat - Cache File System statistics

SYNOPSIS

       /usr/bin/cachefsstat [-z] [path...]

DESCRIPTION

       The  cachefsstat command displays statistical information about the cache file system mounted on path. The statistical information includes
       cache hits and misses, consistency checking, and modification operations. If path is not specified, all	mounted  cache	file  systems  are
       used.

       cachefsstat can also be used to reinitialize this information (see -z option).

       The statistical information has the following format:

       <cache hit rate>
       <consistency checks>
       <modifies>
       where:

       hit rate 	       The percentage of cache hits over the total number of attempts, followed by the actual numbers of hits and misses.

       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, including writes, creates, etc.

OPTIONS

       The following option is supported:

       -z	Zero  (reinitialize)  statistics. Execute cachefsstat -z before executing cachefsstat again to gather statistics on the cache per-
		formance. This option can only be use by the superuser.  The statistics printed reflect  those	just  before  the  statistics  are
		reinitialized.

USAGE

       See largefile(5) for the description of the behavior of cachefsstat when encountering files greater than or equal to 2 Gbyte (2**31 bytes).

EXAMPLES

       Example 1: Using cachefsstat

       The following example shows the cachefsstat command run on file system /test:

       example# cachefsstat /test
	 /test
	      cache hit rate:	   100% (0 hits, 0 misses)
	      consistency checks:    0	(0 pass, 0 fail)
	      modifies: 	     0
       garbage collection:	     0

EXIT STATUS

       The following exit values are returned:

       0	       Successful completion.

       non-zero        An error occurred.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cachefslog(1M), cachefswssize(1M), cfsadmin(1M), attributes(5), largefile(5)

SunOS 5.10							    9 Oct 2003							   cachefsstat(1M)