Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 60)

50 Brocade Virtual ADX Global Server Load Balancing Guide
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Configuring GSLB protocol parameters
1
Changing the session-table capacity threshold and tolerance values
You can change the following parameters associated with the session-table metrics:
• Session capacity threshold – Specifies how close to the maximum session capacity the site
ADX device (remote ADX device) can be and still be eligible as the best site for the client. This
mechanism provides a way to shift load away from a site before the site becomes congested.
The default value for the threshold is 90%. Thus a site ADX device is eligible to be the best site
only if its session utilization is below 90%.
• Available session capacity tolerance – Specifies the percentage by which the number of
available sessions on the site ADX device can differ from the number of available sessions on
another site ADX device and still be considered an equally good site.
You can change these parameters on an individual basis.
To change the session-table capacity metric, enter commands such as the following.
Virtual ADX(config)#gslb policy
Virtual ADX(config-gslb-policy)#capacity threshold 99
Syntax: [no] capacity threshold num
The num parameter specifies the maximum percentage of a site ADX device’s session table that
can be in use. If the Brocade Virtual ADX’s session table utilization if greater than the specified
percentage, the GSLB Brocade Virtual ADX prefers other sites over this site. You can specify a
percentage from 0 – 100. The default is 90.
To change the session-table tolerance metric, enter commands such as the following.
Virtual ADX(config)#gslb policy
Virtual ADX(config-gslb-policy)#num-session tolerance 20
Syntax: [no] num-session tolerance num
The num parameter specifies the maximum percentage by which the session table utilization on
ADX devices at different sites can differ without the GSLB Brocade Virtual ADX selecting one over
the other based on this metric. You can specify a tolerance from 0 – 100. The default is 10.
Changing the FlashBack tolerance values
You can modify the following FlashBack parameters:
• Application tolerance
• TCP tolerance
The GSLB Brocade Virtual ADX uses a tolerance value when comparing the FlashBack speeds of
different sites. The tolerance value specifies the percentage by which the FlashBack speeds of the
two sites must differ in order for the Brocade Virtual ADX to choose one over the other. The default
FlashBack tolerance is 10%. Thus, if the FlashBack speeds of two sites are within 10% of one
another, the Brocade Virtual ADX considers the sites to be equal. However, if the speeds differ by
more than 10%, the Brocade Virtual ADX prefers the site with the lower FlashBack speed.
FlashBack speeds are measured at Layer 4 for all TCP/UDP ports. For the application ports known
to the Brocade Virtual ADX, the FlashBack speed of the application is also measured.