Stacker and Disk Caching Programs

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STACKER NOTE                                                   STACKER NOTE

Title: Stacker and Disk Caching Programs

STAC FAX Index #2401 - 6/18/92                          

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Background.

   Stacker has been tested with most popular disk caching programs such as   

   Smartdrive, PC-Kwik, PC-Cache, Norton Cache, and HyperDisk, and has been 

   found to be compatible.  These programs will cache the Stacker drive, but 

   not directly.  A Stacker drive is actually cached by caching the physical 

   drive which hosts the drive's companion STACVOL file.  As a bonus, by 

   caching this file and it's compressed data, the cache size is effectively 

   doubled. 

   For example, let's say you have Stacked your C: drive.  You can use the 

   Stacker program to determine the host drive.  

   Type: C:\STACKER\STACKER     <ENTER>        

   The output will look similar to: 

   STACKER -  Stac Electronics, Carlsbad, CA

   

   Drive C: was drive D: at boot time  [ D:\STACVOL.DSK = XX.X 0MB ]

   Drive D: was drive C: at boot time  

   This drive map tells us that D: is the host for the C: Stacker drive.  

   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 

   25 MB STACVOL.DSK file and therefore your C: drive.  

Do I need to tell the caching program not to cache the Stacker drive?

    Most disk caching 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 a message such as "unable to cache specified drive".     

    To be sure, you should examine the status of the cache to ensure that it

    is in fact caching only the physical drives.  If you are given the option 

    of drives to cache, specify the host 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\SMARTDRIVE.EXE  D 

   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 before the Stacker device driver 

       (if it loads in Config.sys.)    

         -OR- 

    2. If the cache loads in Autoexec.bat, add a space, then an '@' 

       (without the quotes) to the end of the Stacker device driver in 

       Config.sys for each drive you wish to mount as replaced.  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 or lazy write,  causes the data 

    to be held in memory for a period of time before it gets stored to disk.  

    This technique enables greater efficiency, however, if the machine hangs 

    or is rebooted before the information is written to disk, data is lost or 

    possibly corrupted.  A Stacker drive will not increase the likelihood of 

    file corruption occurring. However, it is just as susceptible as any other 

    DOS disk.  It is up to you to determine if the extra speed is worth the 

    risk.  The write delay feature is usually selectable, and can therefore be 

    disabled.  For example, with SMARTDRIVE 4.0 disable write caching by 

    placing the host drive letter ONLY on the command line.  For example,

       

    C:\WINDOWS\SMARTDRV.EXE  D    (where D is the host drive letter)

Can I use Stacker's cache with other caches?

    Stacker gives you the option of setting up a small cache in EMS or 

    conventional memory.  The 64K EMS cache will provide caching benefits and 

    greatly reduce the Stacker device memory requirements.  Alternatively, 

    the conventional memory cache of 0 to 64K can be setup with a /m=x 

    parameter (where x=0-64) on the Stacker device driver in Config.sys. 

    Unlike the EMS cache, this adds directly to the size of the driver.  The 

    default for the conventional memory cache size is 0 K.  Both caches are  

    compatible with third party caches but due to their relative small size, 

    their contribution is negligible.  Because of this, in the presence of 

    another cache, there is really no need to enable the Stacker cache unless

    you desire to use the EMS cache for reducing the device driver size.  

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Copyright 1993, Stac Electronics