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How a probe uses RAM
Chapter 14: Understanding How a Probe Uses RAM 309
Figure 143: How to resize various memory options
Packet capture buffer and statistics buffer
There are two kinds of buffers that a probe uses to store data in real-time:
capture buffers and statistical buffers. The capture buffer stores the raw data
captured from the network while the statistical buffer stores data entries that
are snapshots of a given statistical data point.
Selecting an appropriate capture buffer size given system resources is all most
users need to worry about; the default settings for the statistical buffers work
perfectly fine in the vast majority of circumstances.
However, if you are pushing the limits of your probe system by creating many
probe instances, you may be able to avoid some performance problems by fine-
tuning the memory allocation for each probe instance.
For example, suppose you want to give a number of remote administrators
access to Top Talkers data from a given probe. You will be able to add more probe
instances within a given system’s memory constraints if you set up the statistics
buffers to only allocate memory for tracking Top Talkers and to not allocate
memory for statistics that no one will be looking at.
Observer has no limitations on the amount of RAM that can be used for a buffer.
Note that when run on a 64-bit Windows, there is no 4 GB limitation for the
capture buffer; you are limited only by the amount of physical memory installed
on the probe.
In all cases, the actual buffer size (Max Buffer Size) is also reduced by 7% for
memory management purposes. Should you try and exceed the Max Buffer Size
an error dialog will be displayed indicating the minimum and maximum buffer
size for your Observer (or probe) buffer.
For passive probe instances, which are most often used for troubleshooting, the
default settings should be sufficient. If you are creating an active probe instance
(one that writes to disk and not just reads from it), then you may want to use the
following formula as a rough guideline to determine how much RAM to reserve