Product guide

11
ATTO Technology Inc. ExpressPCI UL5D, UL4S, UL4D Host Adapter Installation and Operation Manual
6 Maximizing performance in Windows
If you are getting less performance than you expect, there are several things you can do such as making
sure you are using the latest ATTO driver, setting the registry entry for large block transfers, using
ATTO ExpressRAID for setting up RAID groups, increasing transfer size, and analyzing your system’s
I/Os.
While the factory settings on your ExpressPCI
host adapter should provide excellent
performance for a wide range of applications, you
may improve performance by modifying some of
the system factors which affect your ExpressPCI
host adapter.
For example, the ATTO driver can transfer well
over a megabyte with one SCSI command.
Note
You must use an ATTO driver when using
ATTO ExpressRAID software.
This procedure is available for Windows only.
Use the latest ATTO driver
Determine which drive is currently in use, then
install the latest ATTO driver found at
www.attotech.com .
1 Using the Device Manager, select SCSI &
RAID Controllers
2 Examine the Driver tab for your SCSI adapter.
If the driver is not express2.sys, install the
express2.sys driver.
3 Either remove the previously-installed driver or
disable it using the Devices applet. If the
system has a built in Symbios or LSI adapter,
do not disable the driver for that adapter.
Set registry for large block transfers
If your application requires large block transfers,
set the registry entry correctly for the
MaximumSGList keyword. Several files supplied
with the device driver download package can set
values in the range of 64KB to 8MB. The files are
ASCII text files with .reg extension and can be
viewed with any suitable editor. The files also
explain the registry setting and how to change the
setting.
Set up RAID groups
Instead of using the RAID functionality built into
Windows OS, use the ATTO ExpressRAID
software for the most efficient performance.
ATTO ExpressRAID requires one less level of
driver through which commands must pass and
fewer commands are required to pass through the
driver hierarchy.
Other advantages of ATTO ExpressRAID
striping:
• You can boot your system off striped drives
• Stripe sets created with ExpressRAID are
recognizable by DOS and Windows
• You can stripe removable-media drives with
ExpressRAID.
If you have purchased the striping option,
additional information about ExpressRAID is
available in the file Stripe.txt on the CD which
has been included with your ATTO ExpressPCI
adapters.
Increase transfer size
If you are writing to an application that uses a lot
of sequential disk I/O to a contiguous area on
disk, you should use as large a transfer size as
possible to reduce overhead on the system, on the
SCSI bus and within disk drives.
Analyze your I/Os
For large sequential data transfers, use Direct
I/O by selecting
FILE_FLAG_WRITE_THROUGH and
FILE_FLAG_NO_BUFFERING flags with
your CreateFile call to avoid the overhead of
copying data from one area of memory to another,
to reduce the number of SCSI commands which
must be executed and to leave system pages
available for other data.