EDM01-02: DAG 4.2S Card User Guide
©2005
22
Version 7: May 2006
Detecting
packet losses
Until some data is read out of the buffer to free some space, any arriving
packets subsequently will be discarded by the DAG card. Any loss can be
detected in-band by observing the
lctr
[Loss Counter] field of the
Extensible Record Format.
Avoiding packet
loss
In order 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 may be required per card.
The amount of memory reserved is changed by editing the file
/etc/modules
. If the Endace Install CD has been used it will include this
section
# 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 must be less than
890MB.
