The World of Computer Software/The World of Computer Software.iso/stac0193.zip/TEC009.DOC

Text File | 1992-11-03 | 6KB | 110 lines

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STAC FAX                                                           STAC FAX

Title: Stacker and Disk Caching Programs

STACKER NOTE TEC009 - 6/18/92                          STAC FAX Index #2401
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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 - 2.00, (c) 1990-91, 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 1992, Stac Electronics                    STAC FAX [phone]