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NOVELL TECHNICAL INFORMATION DOCUMENT
TITLE: Configuring NWCACHE
DOCUMENT ID: 014926
DOCUMENT REVISION: B
DATE: 27APR94
ALERT STATUS: Yellow
INFORMATION TYPE: Issue
README FOR: NA
NOVELL PRODUCT and VERSION:
Novell DOS 7
ABSTRACT:
NWCACHE is a disk cache with many different configurations
options available. This document discusses some of the
configuration options available for NWCACHE.
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DISCLAIMER
THE ORIGIN OF THIS INFORMATION MAY BE INTERNAL OR EXTERNAL TO
NOVELL. NOVELL MAKES EVERY EFFORT WITHIN ITS MEANS TO VERIFY
THIS INFORMATION. HOWEVER, THE INFORMATION PROVIDED IN THIS
DOCUMENT IS FOR YOUR INFORMATION ONLY. NOVELL MAKES NO EXPLICIT
OR IMPLIED CLAIMS TO THE VALIDITY OF THIS INFORMATION.
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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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complete trademark information.
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