___________________________________________________________________________ STACKER NOTE STACKER NOTE Title: Stacker and Disk Caching Programs STAC FAX Index #2401 - 6/18/92 ___________________________________________________________________________ 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 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. ___________________________________________________________________________ Copyright 1993, Stac Electronics