Specifications
Page B-5Read-Ahead and Write Buffering
When specifying write buffering for a device, two files are loaded into system memory:
.DVR and .WRC, which are the driver and cache buffer. This is true for all SCSI disk
devices except the DSK device. For the DSK device, the file DSK.DVR does not need to
be created because it is already loaded into the system monitor. Therefore, for the DSK
device, only the file DSK.WRC will be loaded into system memory.
The buffer-size is the size of the write buffer (you specify the size in Kilobytes).
Specifying a buffer size of over 100KB is unlikely to improve performance.
The flush-period is the absolute maximum number of seconds data may be left in the
write buffer without being written to the disk. For example, if you specified 30, you would
know that after 30 seconds any pending writes would be written to the disk. This is true
even if the disk is constantly busy servicing reads.
In the three drive example mentioned earlier, the added SYSTEM commands would
look similiar to this:
SYSTEM DVR:DSK/N 100K 60 ;Driver in AMOS will create DSK.WRC
SYSTEM DVR:SUB/N 100K 60 ;Load SUB.DVR and create SUB.WRC
This would set up 100KB of write buffering for the DSK devices and 100KB of write
buffering for the SUB device. All three drives would have their write buffers flushed
every minute (or sooner if the drives are not busy with read requests).
B.4FINAL NOTES
Both read-ahead and write buffering schemes used on the AM-137 hardware
dramatically improve system performance in our lab tests. Both schemes are fine tuned
for both the 68030 processor and RISC SCSI controller and do not take cycles away
from AMOS like other commercially available disk optimization software.
Although our lab tests attempt to simulate the "real world" of user applications, they
probably use the resources of the AM-137 CPU and SCSI sub-system completely
differently than your application does, therefore we highly recommend you experiment
with both cache and write buffer sizes, read-ahead blocks and flush periods on an
installed system to find the best possible combination for that system.
B.4.1Sample AMOS32.INI File
On the next two pages, a sample system initialization command file is shown with the
key AM-137 related statements highlighted in bold type. At the bottom of each of the
example pages, there is additional information for each of the bolded entries.
PDI-00137-50, Rev. A01