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OS/2 Shareware BBS: 8 Other
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1994-04-08
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4KB
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108 lines
Fri 94-04-08
=============
Note, the original version of this program (released August, 93) was
pulled just a few days after release. It caused kernel traps in systems
with moderate to heavy swapping activity. After sitting on the shelf
for many months, I discovered that the bug was in the OS/2 kernel
itself. This updated version appears to work perfectly with the latest
OS/2 service pack installed (ie: OS/2 2.11, Syslevel XR06200).
Do not attempt to use this program with OS/2 2.0 or OS/2 2.1 (without
the service pack).
If you are using OS/2 2.11 and see a kernel trap with this program, I
would like to hear about it.
=============================================
SwVdisk.sys is a modified version of OS/2 2.1's VDISK.SYS; it uses
swappable memory.
The normal VDISK.SYS allocates "fixed" memory to create a virtual disk.
This is the proper way to create a Vdisk, if you are creating it for
performance reasons. A vdisk is almost always created for this reason.
Since OS/2 has such a great disk cache (especially for HPFS) built in,
it is almost always better to give memory destined for a VDISK to your
disk cache.
A large vdisk, with what you think are your most-used files copied on
to it, is nothing more than a "non-dynamic disk cache". This procedure
is, put bluntly, a feeble idea for OS/2 systems. It would be better
to give that memory to a good dynamic disk cache, like the one built in
to OS/2.
A large swappable vdisk, created with intended performance gains, is
downright doltish. The system will have to swap out (to a real disk)
memory when you access the vdisk; in the end your vdisk is stored on
your hard disk. Some people have had crazy ides for vdisk's (like
storing swapper.dat on one!).
Why a swappable vdisk then? Other vdisk uses include:
o Temporary storage. I place files on my vdisk all the time, glad
that they will disappear after rebooting.
o Transitional files. I tell some C compilers to use it for
transitional files (which the compiler frequently forgets to erase:
Compiler Turds, Keith calls them).
o Testing. Sometimes I install software on my vdisk, if I don't trust
the installation process. Sometimes I test software that I have
written myself, but don't trust yet, on a vdisk.
Non of these reasons are performance based.
With the "fixed" memory vdisk, I found myself not wanting to create a
vdisk of more than 256kb-512kb, since the operating system work space,
or the disk cache, can put the memory to better use. Occasionally,
however, I found that I needed a larger vdisk.
I was happy that IBM included the source code for VDISK.SYS on the DDK
CDROM (Device Driver Kit). It has been rewritten to use some of the new
features of OS/2 2.x, namely, large memory objects via VMAlloc(). It
was pretty easy to change it to use swappable memory.
I now use SwVdisk.sys as a 1MB disk drive. The 1MB does not 'steal'
memory from my disk cache, and is only used when I use the drive.
SwVdisk.sys is installed the same way VDISK.SYS is (type "HELP VDISK" at
any command prompt). You can create a vdisk as large as 8192k with it,
but this is not recommended; it will cause your system to do a lot of
swapping. Used incorrectly, SwVdisk can seriously inhibit performance.
Unless you have MEMMAN=COMMIT in config.sys, the memory used by SwVdisk
will not be reserved until you use it. Therefore, even if you ask for
an 8MB vdisk, you won't see your SWAPPER.DAT file grow until you start
to use the vdisk.
Copyright (c) 1993 A:WARE Inc.
DISCLAIMER
----------
The Program is supplied "AS IS" without any warranty of any kind,
either expressed or implied, including, but not limited to, the
implied warranties of merchantability and fitness for a particular
purpose.
In no event shall A:WARE INC be liable for any damages, either
direct or consequential, caused by the use, or inability to use,
this program, even if A:WARE INC has been advised of the
possibility of such damages.
There is no charge for the use of this program.
A:WARE Inc. develops custom applications, file systems, device drivers
and utilities for OS/2.
A:WARE Inc.
6056 Cayeswood Ct.
Mississauga Ontario
Canada L5V-1B1
Voice: (905)858-3222
FidoNet: 1:259/414
BBS: (905)858-8488