TITLE:              Configuring NWCACHE
DOCUMENT ID:        TID14926
DOCUMENT REVISION:  2
DATE:               27APR94
ALERT STATUS:       Yellow
README FOR:         NA

NOVELL PRODUCT and VERSION:
Novell DOS 7

ABSTRACT:
NA

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ISSUE:

NWCACHE loads with parameters specifying the maximum cache size, the
minimum cache size, whether memory lending is enabled, and whether
write delays are enabled.  These and other parameters can be
specified when NWCACHE is loaded; NWCACHE /? will show the possible
values.

If no values are specified, NWCACHE will determine the type and
amount of memory available on your system and load with the
appropriate values.  By default, write delays will be set to off.  If
the necessary memory is available, memory lending will be set on, and
the maximum and minimum cache size will differ by the amount of
memory that NWCACHE can lend.

SIZE OF CACHE

Using the DPMS specification, NWCACHE moves a portion of its code
into extended memory.  It also automatically attempts to put some
code in upper memory.  Therefore, you do not need to use HILOAD or
HIINSTALL when loading NWCACHE.  The NWCACHE code "footprint" is 5 KB
(10 KB if DPMS is not used), and the look-ahead buffer typically
requires 4 to 16 KB.

If you are using expanded memory (EMS) for the cache buffer, use the
/BE switch if you wish to minimize the effect of NWCACHE on your
conventional and upper memory.  This switch locates the look-ahead
buffer into EMS memory.

If you are using extended memory (XMS), load DPMS.EXE before NWCACHE
and use the /MLX or /MUX (default) switch when loading the cache
program.

The memory optimization described above for EMS and XMS will not
necessarily yield the most efficient (fastest) cache configuration
for every system, so you will need to experiment to see what works
best on your system.

The maximum allowable size for the NWCACHE buffer is 7 MB. If you
specify a cache buffer greater than 7 MB, only 7 MB will be allocated
to NWCACHE.

USING NWCACHE AND WINDOWS 3.1

Disk caching with NWCACHE is recommended for improved performance
with Windows.  NWCACHE needs to be loaded before starting Windows,
DesqView /X, or any other multitasking software.  While Windows is
active, diskette drives are temporarily switched from buffered write
to write-through mode.

Although, NWCACHE attempts by default to use all available extended
memory (up to 7 MB), it lends back memory to applications, as
requested.  The amount of memory that NWCache can lend to an
application is determined by the difference between the maximum size
of the cache and the minimum size of the cache, as allocated when
NWCache is loaded.

For example, if the maximum cache size is set to 4096 and the minimum
cache size is set to 1024, the amount of memory available for lending
to other applications is 4096 to 1024, which equals 3072 KB or 3 MB.

Windows is unique in that it allocates all extended memory when it is
loaded.  Other applications use varying amounts of extended memory as
they need it.

Windows needs 2 MB or more of memory to run efficiently in enhanced
mode.  If your system has less than 4 MB of memory, you need to force
NWCACHE to lend at least 2 MB of extended memory back to Windows.  To
do so, set the minimum cache size to be at least 2048 KB smaller than
the maximum cache size, and set the /LEND switch to /LEND=ON.  An
example of this configuration would be to load NWCACHE with the
following parameters:

     NWCACHE 3072 1024 /LEND=ON

If you run several applications through Windows and run out of
memory, you can increase the amount of memory that NWCACHE can lend
by decreasing the minimum cache size.

For example, to lend 4 MB of memory, make the minimum cache size 4096
KB smaller than the maximum cache size (and set the /LEND switch to
ON).

If your system has a lot of memory (8 MB or more) and you use Windows
extensively, turn off lending completely and set a maximum size for
the cache buffer, leaving ample memory free for Windows.

For example, on a system with 10 MB total memory (9 MB extended),
load NWCACHE with the following switches: NWCACHE 3072 1024
/LEND=OFF.  This allocates 3 MB of memory to the cache, leaving 6 MB
of extended memory untouched, so that Windows can have 6 MB for its
own use. If you find that Windows is still running out of memory,
enable lending (/LEND=ON).

USING NWCACHE WITH NETWORKS

NWCACHE can be used on a DOS network workstation or on a PERSONAL
NetWare Server.  Some disk caches that do delayed writes will cause
hanging or corruption on a PERSONAL NetWare server; however, NWCACHE
has been specifically designed to be aware of Novell's peer-to-peer
server software.  Load NWCACHE before any network is started. NWCACHE
will not cache remote network drives (such as, drives across the
network).

If you are running NWCACHE on a system that runs peer-to-peer network
server software OTHER THAN Novell's PERSONAL NetWare server, you
should consult that network's documentation for information on
running with a disk cache.

GENERAL TIPS

Do not use the Novell DOS VERIFY=ON command when using a network, as
it will negate any gain from caching.  In AUTOEXEC.BAT, set VERIFY=
to VERIFY=OFF.

When using NWCACHE, set the FASTOPEN command in the CONFIG.SYS file
to FASTOPEN=0.  A BUFFERS setting of 4 (BUFFERS=4) in the CONFIG.SYS
file is adequate.

NWCACHE should be loaded early in the AUTOEXEC.BAT file before the
network is loaded.  Any TSRs loaded after NWCACHE must be unloaded
from memory before NWCACHE can be unloaded (with the /Q or /U
switch).

TROUBLESHOOTING NWCACHE

As is the case with any software cache, NWCACHE should not be run
concurrently with other disk caches.  If NWCACHE is enabled, verify
that no other disk cache is running.

If the factors listed here have been eliminated and NWCACHE does not
function, adjusting the parameters used when loading NWCACHE is
probably necessary.  Begin with the simplest settings.

For example:

     NWCACHE /LEND=OFF   /DELAY=OFF

If an application seems to need more memory, increase the amount of
memory that NWCACHE can lend to applications.  This can be done by
setting /LEND to /LEND=ON, and decreasing the minimum cache size.

If it appears that NWCACHE is the cause of an upper memory conflict,
use the NWCACHE /L, /ML, and /BL switches to force all parts of
NWCACHE into conventional memory for testing purposes.

If you are experiencing problems reading a drive or if you are
getting data corruption, try disabling delayed writes. This is done
by placing /DELAY=OFF on the NWCACHE command line.  Alternatively,
you can use /x:- switch (where x is the drive letter), to disable
caching on that drive.

If your drive controller or adapter has a built in disk cache, you
should consult its documentation or technical support for information
on using software disk caches.  Most likely, you will not benefit
from NWCACHE. In any case, if you run NWCACHE, you should disable the
controller's cache. However, you will get better use of memory if you
allow the controller to cache the drive; you will be able to use your
extended or expanded memory for other purposes.

Some SCSI drives may require that your cache supports double
buffering of disk transfers.  To enable this, load the DBLBUF.SYS
driver in the CONFIG.SYS file. The DBLBUF.SYS driver will require 2
KB of conventional memory, and it needs to be loaded in the
CONFIG.SYS file after any lines that load memory device drivers or
network device drivers. Do not load DBLBUF.SYS high.

The following information was taken from a technical discussion of
some situations when double buffering might be needed.  Our technical
support department has no clarification for the information presented
below.  Keep in mind that this information has NOT been verified by
Novell:

     Only some older SCSI controllers that do not use the Virtual DMA
services require DBLBUF.SYS to be loaded before NWCACHE; newer SCSI
controllers are safe. Multimaster disk controllers and hard disks
that use DMA for disk transfers, such as PS/2, might also require
double buffering. INSTALL does not test the system for such
controllers. NWCACHE will do a simple test by reading one sector both
into upper and conventional memory and will refuse to load if any
differences in data read were found, but this may not yield
conclusive results.

     The general advice would be: if NWCACHE displays the message
that DBLBUF.SYS is required, load DBLBUF.SYS at the beginning of
CONFIG.SYS (before or after EMM386.EXE).  Otherwise, load DBLBUF.SYS
if you experience problems reading/writing to the disk.  It would be
wise to do a CHKDSK or similar read-only operation that cannot trash
the disk before you find out that double buffering is required.  If
NWCACHE is not loaded into upper memory (/ML[X] and /BL), double
buffering will not be required.

     If using MS Windows or TASKMGR, however, double buffering might
be required even if the cache is loaded low or not loaded at all.

     Previously, there was a "safe-but-slow" setting for disk
deblocking in IBMBIO.COM. This has been changed to a
"fast-but-dangerous" setting (as used by MS DOS).

     The old default value at which IBMBIO started single sector
deblocking was A000 (that is, 640 KB).  This had a speed penalty for
things loaded into upper memory (such as STACKER, SERVER).  You could
always say DEBLOCK=FFFF in CONFIG.SYS.

     The new default value is FFFF, so you get the higher
performance.  The down side is you may get disk corruption. Be
especially wary of multi-master disk controllers, hard disks that use
DMA (PS/2's mostly), and anything to do with floppy transfer.  You
may have drivers supplied with the card (such as ASPI4DOS.SYS); if
so, use them.  You can also use the double buffering driver supplied
with NWCACHE, or add DEBLOCK=A000 in CONFIG.SYS.

SUMMARY

This document covered some of the configuration options for use of
NWCache.  Step-by-step information can be found in the NWCache
HotStart.  Further information can be found in the Novell DOS 7 User
Guide, in DOSBOOK, and in the Novell ASK Information System.

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