Endace DAG 3.7D, User Manual

Page: 22 / 33

EDM01-06: DAG 3.7D Card User Guide
©2006 16 Version 1: March 2006
High Load
Performance
(cont.)
Detecting Packet Losses
Until some data is read out of the buffer to free some space, any arriving
packets subsequently are discarded by the DAG card. Any loss is detected
in-band by observing the Loss Counter
lctr
field of the Extensible
Record Format [ERF]. See Chapter 6 of this Guide for more information on
the Endace ERF.
Reading Records
To avoid any potential packet loss, the user process must read records faster
than they arrive from the network.
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.
Increasing Buffer Size
The host PC buffer can be increased to deal with bursts of high traffic load
on the network link.
By default the
dagmem
driver reserves 32MB of memory per DAG card in
the system. Capture at OC-12/STM-4 (622Mbps) rates and above may
require a larger buffer.
128MB or more is suggested for Linux/FreeBSD.
For the DAG 3.7T card Windows operating system the upper limit is
32MB.
In Debian Linux the amount of memory reserved is changed by editing file
/etc/modules
:
# For DAG 3.x, default 32MB/card
dagmem
#
# For DAG 4.x or 6.x, use more memory per card,
E.G.
# dagmem dsize=128m
The option
dsize
sets the amount of memory used per DAG card in the
system.
The value of
dsize
multiplied by the number of DAG cards must be less
than the amount of physical memory installed, and less than 890MB.