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STACKER NOTE                                                   STACKER NOTE
Title: Stacker Drive Space Reporting
STAC FAX Index #2602 - 2/10/93                          
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Background.

   Use Stacker 2.0's SCHECK or Stacker 3.0's CHECK /D utility to see exactly 
   how the space has been used in the Stacker drive.    

   Here is an example of an SCHECK & CHECK /D report:

   Volume in drive C is STACVOL_DSK
   No errors found
   Stacker Drive Statistics:

                  Stacker Drive             STACVOL File
                  Drive C:                  D:\STACVOL.DSK
                 -------------------       --------------------
   Total Bytes:  4,109,312                   2,054,656
   Bytes Used:   3,735,552 ( 91.2%)          1,846,272 ( 89.9%)
   Bytes Free:     373,760 (  8.8%)            208,384 ( 10.1%)

   Stacker Drive Compression Ratio = 2.0:1
   Projected Bytes Free            = 373,760


What does it all mean?

   The Left Hand Column:  This column displays "logical" data in the clusters 
   on the Stacker drive.  In this example, it tells us that there are enough 
   allocation units (clusters) for 4 MB of data.  There are enough clusters 
   left to acomodate 373,760 bytes of data.  The DOS CHKDSK program 
   reports these numbers because it looks at allocation units.  

   The Right Hand Column:  This column shows the usage of actual physical 
   hard disk space inside the STACVOL.DSK file.  The Stacvol file contains 
   all of the data and free space for the Stacker drive C:.  It's name and 
   location are shown in the column title.  In our example, D:\STACVOL.DSK is 
   2 MB in size and has used all but 208,384 bytes of that 2 MB.  Therefore, 
   there are 208,384 bytes of physical free space left in D:\Stacvol.dsk.    

Compression ratio.
   
   The Stacker drive compression ratio indicates the average compression of 
   the files in that drive.  The compressibility of the files is generally 
   dependent on their contents.  In the above example, the 2.0:1 ratio tells 
   us that the files in this Stacker drive are taking up half the space they 
   would take up on a "Non-Stacked" drive. (A 2.0:1 ratio is typical for an 
   average mixture of files.)  A drive full of graphics files may achieve an 
   average compression of 8.0:1 or more.  An 8.0:1 ratio would mean that the 
   files are taking up 1/8 the space they would on a standard drive.  
   Conversely, some files are already compressed, such as "zipped" files.   
   Stacker will not attempt to compress previously compressed files, so they 
   will bring down the overall compression ratio of the Stacked drive in 
   which they reside.

   NOTE: The drive compression ratio does not display if the drive is empty.

Projected bytes free.
   
   This number is Stacker's estimate of the available space left on the 
   Stacked drive.  It is determined by multiplying the physical free space 
   (right side) by the compression ratio, OR by the number of clusters left 
   unallocated (left side).  The projected bytes free is limited to the 
   smaller of these two values.  
   
   In our example, physical space free multiplied by the compression ratio 
   would be: 208,386 x 2.0 or 416,772 bytes. However, we only have 373,760 
   bytes worth of unallocated clusters.  Since the projected bytes free is 
   the smaller of these two numbers, it is 373,760.  Fortunately, you can 
   increase the number of allocation units by "growing" the drive.  To grow 
   the Stacker drive, run the Grow & Shrink utility from the STAC command 
   assistant.  "Growing" the drive in this example would increase the             
   projected free space to 416,772.
   
   Notes:  When the number for physical bytes free goes to zero, the drive is 
   full.  You cannot "grow" the drive to create more physical space.  Also, 
   if the drive is less than 12% full, the projected bytes free will equal 
   the "logical" bytes free number (left column). 

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Copyright 1993, Stac Electronics                    
