Avago Technologies LSI SAS 3041E-R - Manual (Page 30)

2-8 Windows Driver Installation
Version 1.3 Copyright © 2001, 2002, 2007 by LSI Logic Corporation. All rights reserved.
2.2.6.1 Large Block Size Support
The SYMMPI.SYS driver can support up to a 1 Mbyte transfer size in
Windows XP; however, the default Windows XP transfer size is
64 Kbytes. To enable better performance, the driver installation process
adds a registry entry to enable the maximum 1 Mbyte transfer size. Also,
the
mpi_256K.reg file can be used to set or enable a 256 Kbyte
maximum transfer size, and it can be edited to set other maximum
transfer sizes as well. There are two ways to add this registry setting:
•
Locate the mpi_256K.reg data file using Windows Explorer, double-
click on the file, and edit it.
•
Type the following at the command prompt:
regedit mpi_256K.reg
This command inserts an entry in the registry to enable 256 Kbyte
block size support.
By editing mpi_256K.reg , you can set any maximum block size between
64 Kbytes and 1 Mbyte. The formula to calculate the proper value for
MaximumSGList in a 32-bit OS is:
MaximumSGList = ((Maximum Block Size)/4 Kbytes) + 1
For example, to determine the MaximumSGList value for 256 Kbytes in
a 32-bit OS, take ((256 Kbytes/4 Kbytes) +1) = 65 (or 0x41 in
hexadecimal).
The maximum value allowed for MaximumSGList is 0xFF (255 decimal).
For the particular value of 0xFF, the internal value passed to Windows
XP is increased to 0x101, allowing support for a full 1 Mbyte transfer.
Read the information in the mpi_256K.reg data file before editing it. You
must reboot the system for the new registry setting to take effect.
For 64-bit systems, the OS page size is 8 Kbytes instead of 4 Kbytes.
Therefore, the maximum transfer size is 2 Mbytes, and the default driver
installation enables support for 512 Kbytes transfer size. The formula to
calculate the MaximumSGList is:
MaximumSGList = ((Maximum Block Size)/8 Kbytes) + 1
To reset the maximum block size to the default of 64 Kbytes, follow the
instructions above, except use
mpidfblk.reg as the data file.