

              NOVELL TECHNICAL INFORMATION DOCUMENT

TITLE:              Stacker Statistics
DOCUMENT ID:        014920
DOCUMENT REVISION:  A
DATE:               25FEB94
ALERT STATUS:       Yellow
INFORMATION TYPE:   Issue
README FOR:         NA

NOVELL PRODUCT and VERSION:
Novell DOS 7

ABSTRACT:

This document explains the statistics shown on a Stacker
compressed partition under Novell DOS 7.

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THE ORIGIN OF THIS INFORMATION MAY BE INTERNAL OR EXTERNAL TO
NOVELL.  NOVELL MAKES EVERY EFFORT WITHIN ITS MEANS TO VERIFY
THIS INFORMATION.  HOWEVER, THE INFORMATION PROVIDED IN THIS
DOCUMENT IS FOR YOUR INFORMATION ONLY.  NOVELL MAKES NO EXPLICIT
OR IMPLIED CLAIMS TO THE VALIDITY OF THIS INFORMATION.
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ISSUE

     This document is not designed to be an introduction to the
     Stacker portion of Novell DOS 7.  Users who are new to
     Stacker should read the following references before reading
     this document:

          Novell DOS 7 User Guide: Chapter 12 "Disk Compression"
          Novell DOS 7 README.TXT
          Stacker section within the DOSBOOK online reference
          manual
          (Type DOSBOOK STACKER at the command line.)

     Novell DOS 7 offers three utilities for examining statistics
     on a Stacker drive: DIR, XDIR, and CHKDSK.  Each of these
     utilities is specifically written to understand the internal
     structures of a Stacker drive.  For a list and description
     of switches for these utilities refer to DOSBOOK or type the
     utility name followed by a /? (for example, DIR /?) at the
     command line.


     DIR

     The Novell DOS 7 DIR command has been written to give an
     accurate calculation of free space on a Stacker drive. 
     Please see the Estimated Bytes Free section below for a
     description of how free space is calculated for a Stacker
     drive.



     XDIR

     The Novell DOS 7 XDIR command has been written to give
     compression ratios for each file on a compressed drive as
     well as an average compression ratio for the current
     directory.  An example of an XDIR of the root directory
     follows:

     --a---         355  8.0:1   2-24-94   9:32a  c:autoexec.bat
     --a---          73  8.0:1   2-18-94  10:32a  c:autostac.bat
     ------      56,081  1.4:1   1-26-94   7:00a  c:command.com
     --a---         306  8.0:1   2-23-94  11:43a  c:config.sys
     rs--h-      27,880  1.4:1   1-26-94   7:00a  c:ibmbio.com
     rs--h-      29,684  1.1:1   1-26-94   7:00a  c:ibmdos.com
     DIRECTORY                   2-18-94  10:02a  c:nwclient
     DIRECTORY                   2-18-94  10:02a  c:nwcntl
     DIRECTORY                   2-18-94  10:02a  c:nwdos
     --a---       4,768  8.0:1   1-26-94   7:00a  c:nwdos.386
     DIRECTORY                   2-18-94  11:25a  c:windows
     DIRECTORY                   2-18-94   2:02p  c:wpc20
     DIRECTORY                   2-18-94   2:00p  c:wpwin60
     total files  7   total bytes 119,147   disk free space
     39,997,440
     average compression ratio 1.6:1

     To get an average compression ratio for the entire drive,
     use the command XDIR /S at the root of the Stacker drive to
     include all subdirectories.  The average compression ratio
     figure obtained by doing an XDIR /S is representative of all
     the files on the drive.  This figure is calculated by
     averaging the actual compression ratio for each file on the
     drive.  An example of the last two lines of an XDIR /S
     follows:

     total files 1,304 total bytes 58,252,054 disk free space
     39,997,440
     average compression ratio 1.6:1

     In the example, the average compression ratio of 1.6:1 is
     slightly below the expected compression ratio for the drive
     (fixed at 2.0:1).  This suggests that the files on the
     Stacker drive are taking up slightly more room than
     expected.

     A Stacker drive is most efficient when the average
     compression ratio is as close to the expected compression
     ratio as possible.  Ultimately the average compression ratio
     should not be much higher or lower than the 2.0:1 expected
     compression ratio.

     If the average compression ratio is much lower than 2.0:1
     (as an example 1.2:1), an overabundance of poorly
     compressible data is on the drive.  A user might consider
     taking files that have a compression ratio (found with XDIR
     /S) much lower than 2.0:1 off the drive.

     If the Stacker Drive Compression Ratio is much higher than
     2.0:1 (as an example 8.0:1), an overabundance of highly
     compressible data is on the drive.  A user might consider
     taking files that have actual compression ratio (found with
     XDIR /S) much higher than 2.0:1 off the drive.

     Note:     The expected compression ratio is set at 2.0:1. 
               Therefore, there are twice as many file allocation
               units in the Stacker FAT.

     A Stacked drive with files that compress at a higher ratio
     will use the allocation units at the same rate as files that
     compress at a lower ratio.  Even though a drive may have a
     very high Stacker Drive Compression Ratio, such as 8.0:1,
     you will not be able to store any more data than the
     expected compression ratio of 2.0:1 allows.

     XDIR also gives accurate used and free space information on
     a Stacker drive.  Please see the Estimated Bytes Free
     section below for a description of how free space is
     calculated for a Stacker drive.


     CHKDSK

     The Novell DOS 7 CHKDSK command used with a /D parameter
     will display space usage on a Stacker drive.  An example
     CHKDSK /D follows:

     Volume STACVOL_DSK created Feb-18-1994 10:36

     Checking cluster integrity...

     Stacker Drive Statistics:

                       Stacker Drive           STACVOL File
                       Drive C:                D:\STACVOL.DSK
                   ----------------------   --------------------
       Total Bytes:   162,914,304             61,506,048
       Bytes Used:     61,329,408 ( 37.6%)    37,220,864 ( 60.5%)
       Bytes Free:    101,584,896 ( 62.4%)    24,285,184 ( 39.5%)

       Bytes Per Cluster:       4,096                2,048

       Fragmentation Level         = 0

     Checking FAT integrity...

       162,914,304 bytes total disk space.
            61,440 bytes in 2 hidden files.
           114,688 bytes in 24 directories.
        61,153,280 bytes in 1302 user files.
        39,997,440 estimated bytes free.

             4,096 bytes in allocation unit.
            39,774 total allocation units on disk.
            24,801 available allocation units on disk.

           655,360 total bytes of memory.
           621,216 total bytes of free memory.
           620,240 bytes in largest free memory block.


     Stacker Drive Drive C:

     This column of CHKDSK /D reports information based on the
     estimated compression ratio of all the files on the drive

     being 1.6:1.  These statistics represent logical disk space
     as each figure represents how space on the Stacker drive
     would be used if this were a standard DOS formatted drive.

     In other words, this information is based on one cluster
     being the smallest allocable unit on the drive.  Consider
     the method for reporting statistics in this column to be
     equal to what CHKDSK would display on any normal DOS
     formatted drive.


     STACVOL File G:\STACVOL.DSK

     This column of CHKDSK /D reports information based on actual
     physical disk space used by Stacker.  In other words, its
     information is based on the amount of physical sectors (512
     bytes) used within the STACVOL file after files have been
     compressed.

     Understanding that Stacker can store files at the sector
     level is important.  This is unlike a normal DOS formatted
     drive, which stores files at the cluster level.  Most
     third-party utilities are incapable of reporting actual
     physical disk space use on a Stacker drive.


     Estimated Bytes Free

     This number represents an estimate of the number of bytes
     free on a Stacker drive.  Actual usable space may vary based
     on the compression ratio of the drive (see above note). 
     This estimate is based on the lesser of the two values found
     using Method 1 and Method 2 that follow:

     Method 1: Estimated Bytes Free is found by multiplying the
               bytes free value in the STACVOL File column by the
               average compression ratio (found with XDIR /S). 
               Although the average compression ratio is rounded
               off to tenths, the compression ratio used in the
               calculation is not rounded off.

     Method 2: Estimated Bytes Free is equal to the bytes free in
               the Stacker Drive column.

     Note:     SETUP will allow you to expand or shrink a Stacker
               drive to increase or decrease the amount of space
               on the drive.  However, when the number of bytes
               free in the STACVOL File column is zero, the drive
               is full.

               You cannot expand the drive to create more
               physical space.  Also, if the drive is less than
               12 percent full, the estimated bytes free will
               equal the bytes free value in the Stacker Drive
               column.
