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      STACKER NOTE                                         STACKER NOTE
                            WHAT DOES FATMGR DO?
                  (Applies to Stacker for OS/2 & DOS ver 4)
      STAC FAX  64008 (1/95)
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      BACKGROUND
      
      The FATMGR.EXE program exists to protect against disk full
      conditions. This is because there may be a difference between the
      expected compression ratio and the actual compression ratio of a
      Stacker drive. Stacker defaults to an expected compression ratio
      of 2.0:1, but you can specify any expected compression ratio if
      you expect your data to compress better or worse than that.
      
      The CREATE and SDEFRAG programs use the expected compression
      ratio and the size of the STACVOL file to determine the number of
      File Allocation Table (FAT) entries needed on the new drive. Each
      FAT entry represents a unit of space on a drive. As files are
      added to the logical drive, FAT entries are used up for each
      file. Files that compress at the expected ratio or better do not
      cause problems, because the logical drive runs out of FAT entries
      (space) before the physical drive, and the "out of disk space"
      condition is properly handled by the operating system. Files that
      compress less than the expected ratio use up disk space faster
      than anticipated. Left unchecked, this condition would cause the
      physical disk to fill up before the logical disk. This may result
      in data corruption.
      
      FATMGR.EXE
      
      This is where the FATMGR enters the picture. It compares the
      actual compression ration to the expected compression ratio, and
      when the actual is less expected, it creates a file called
      DONT_DEL.ME. FATMGR modifies the size of DONT_DEL.ME to bring the
      two ratios into alignment.
      
      File Allocation Errors on DONT_DEL.ME
      
      These errors appear sometimes when you run CHKDSK. FATMGR opens
      the DONT_DEL.ME file and modifies its size as needed. If this
      happens when CHKDSK is running, the directory size won't match 
      what the FAT indicates. CHKDSK reports the disparity with a File 
      Allocation Error message.
      
      SOLUTION
      
      Try running SCHKDSK instead. This Stacker command suspends FATMGR
      and then runs OS/2s CHKDSK. The errors should disappear. 
      Alternatively, wait until the disk is quiet, and then run CHKDSK 
      again. If the error reappears, wait another 8 seconds or so and 
      do it once more. The errors should disappear.
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      Copyright 1995 Stac Electronics
