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      STACKER NOTE                                         STACKER NOTE
                          STACKER 4.0 & DISK CACHES                                      

      STAC FAX  4409 (05-02-1994)
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      BACKGROUND
      
      Stacker is compatible with most popular disk caches such as
      SMARTDrive, PC-Kwik, PC-Cache, Norton Cache, and HyperDisk. These
      programs will cache the Stacker drive, but not directly. A
      Stacker drive is actually a large STACVOL file that resides on
      the physical disk. The disk cache will actually cache the
      physical disk, and therefore the STACVOL file. As a bonus, by
      caching this file and its compressed data, the cache size is
      effectively doubled.
      
      Which drive is actually cached?
      
       The "host" uncompressed drive for the Stacker drive (the STACVOL
      FILE) is cached. You can use the Stacker program to determine the
      uncompressed drive.  Type:
      
           C:\STACKER\STACKER <enter>
      The output concerning your compressed drives will look similar
      to:
      
         Drive C was drive x at boot time  [ D:\STACVOL.DSK = 123.4MB]
         Drive D was drive x at boot time
      (Drive  x  will be either C or D depending on whether Stacker is
      Preloading. See StacFax 4516 for details.)
      Note the drive letter in brackets, in this example drive D. Drive
      D is the host uncompressed drive for Stacker drive C. When you
      write to, or read from Stacker drive C, you are really accessing
      STACVOL.DSK on the D drive. By caching D, the programs are
      caching this STACVOL.DSK file and therefore your C drive.
      
      Do I need to tell the caching program not to cache the Stacker
      drive?
      
      Most disk cache programs will only cache the physical drive.
      Normally, they will not cache the Stacker logical drive by
      default, so you will probably not have to add any special
      parameters. In fact, if you attempt to force the program to cache
      the Stacked drive, you will probably receive an error message
      such as "unable to cache specified drive".
      
      If you are given the option of drives to cache, specify the
      uncompressed drive. For example, if you wish to tell SMARTDrive
      4.0 to cache only the D host drive, the command in AUTOEXEC.BAT
      would be similar to the following:
      
              C:\WINDOWS\SMARTDRV.EXE  D
      See the disk cache's documentation for details on its
      configuration.
      
      NOTE:  If your caching program loads in CONFIG.SYS, make sure its
      device driver loads BEFORE the Stacker device driver. This
      insures caching of the host drive only.
      
      How do I cache a "replaced" Stacker drive or removable drive?
      
      A "replaced" Stacker drive is one which has replaced its drive
      letter with that of the host drive.  Removable drives such as
      floppies, Bernoulli drives and Syquest drives are mounted this
      way. In order to cache these replaced drives, they must be
      mounted and replaced after the cache has been loaded. This can be
      done by:
      
       1.  Placing the cache device driver (if it loads in CONFIG.SYS)
           before the Stacker line. This procedure only works for non-
           preloading DOS versions.
           OR
       2.  If the cache loads in AUTOEXEC.BAT, then type ED /I <enter>
           to edit the STACKER.INI file. Add the line /RP=n to the file
           (where n is the number of replaced drives). Press CTRL-Z to
           save the file. Then, in AUTOEXEC.BAT, after the command to
           load the cache, mount each drive (one line for each drive)
           with:
           C:\STACKER\STACKER X:
           where X: is the Stacker drive you wish to mount as replaced.
           
      Is it safe to use a cache's write delay feature with Stacker?
      
      Most caches, such as SMARTDrive 4.0, incorporate a write delay
      feature. A write delay, also known as a write back, write behind,
      or lazy write, causes the data to be held in memory for a period
      of time before it gets stored to disk. This technique makes the
      cache more efficient. But if the machine hangs or is rebooted
      before the information is written to disk, data may be lost or
      corrupted. A Stacker drive will not increase the likelihood of
      file corruption. However, it is just as susceptible as any other
      DOS disk. You must decide if the extra speed is worth the risk.
      The write delay feature is usually selectable, and can therefore
      be disabled. The version of SMARTDrive that comes with MS-DOS 6.2
      has the write delay feature, but it is disabled by default. See
      your cache's documentation for information on disabling the write-
      delay feature if you desire.
      
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      Copyright 1994 Stac Electronics
