Endace DAG 3.7G Series, Руководство пользователя

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EDM01-07: DAG 3.7G Card User Guide
©2005 13 Version 7: May 2006
Chapter 4:
Capturing Data
Starting a
Session
For a typical data capture session follow the steps listed below:
•
Move to the
dag
directory,
•
Load the appropriate driver,
•
Then load the appropriate FPGA image
•
Set the integrity of the card’s physical layer and check the integrity of the
physical layer to each DAG card. For example:
dagthree –d0 dag0 default
•
Engage the failsafe relays using:
dagwatchdog –p –d N
Note: This command is not required on non-failsafe versions of the
card
•
Start the capture session using:
dagsnap -d dag0 –v -o tracefile
Note: You can use the
-v
option to provide user information during a
capture session, although you may want to omit it for automated trace
runs.
By default
dagsnap
will run indefinitely but can be stopped using CTRL+C .
You can also configure
dagsnap
to run for a fixed time period then exit.
High Load
Performance
Overview
As the DAG 3.7T card captures packets from the network link, it writes a
record for each packet into a large buffer in the host PC’s main memory.
Avoiding Packet Loss
To avoid packet loss, the user application reading the record, such as
dagsnap
, must be able to read records out of the buffer faster than they
arrive. If not the buffer will eventually fill and packet records will be lost.
If the user process is writing records to hard disk, it may be necessary to use a
faster disk or disk array. If records are being processed in real-time, a faster
host CPU may be required.
In Linux and Free BSD, when the PC buffer fills, the following message
displays on the PC screen:
kernel: dagN: pbm safety net reached 0xNNNNNNNN
The same message is also printed to
log /var/log/messages
. In addition,
when the PC buffer fills the “Data Capture” LED on the card will flash or
flicker, or may go OFF completely.
In Windows no screen message displays to indicate when the buffer is full.
Please contact Endace Customer Support at support@endace.com for further
information on detecting buffer overflow and packet loss in Windows.