Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 70)

54 Brocade Virtual ADX Server Load Balancing Guide
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Primary and backup servers
2
Syntax: [no] port port-name backup
Per server based real server backup
The current implementation of the backup server requires that all non-backup servers fail before
SLB directs requests to backup servers. This method might not allow for maintaining the same level
of performance in the server farm. The ability to maintain the same performance level for a given
service is critical for many customers.
Per server based real server backup allows the backup servers to be associated with the specified
primary servers. When a primary server fails, its backup server starts processing the traffic no
matter what state the other primary servers are in. This feature works with the current real server
backup mechanism by providing additional control of the backup server selection.
Current backup scheme
Currently, when a primary server goes down another server is selected among the active primary
servers. Until all the primary servers are down, the server is selected from the backup servers.
Additionally, the users can configure backup-stay-active to keep the server selection in the backup
groups active, even when some primary servers come back up.
Per server based backup scheme
With this feature, the associated primary and backup servers back up each other, regardless of the
state of the other service ports. If a backup server is associated with a primary server, they work as
a pair so that each can substitute for the other when it becomes unavailable.
If the backup-stay-active is configured, the backup server continues to process the traffic even
after the primary server comes up again.
Example
Primary servers: A and B
Backup servers: C and D
Backup association: C is backup of A, D is backup of B.
Condition 1: When A goes down and B is alive, the server is selected from C and B.
Condition 2: When both A and B go down, the server is selected from C and D.
Condition 3: if backup-stay-alive is not configured. When B comes up and A stays down, the server
is selected from C and B.
Condition 4: if backup-stay-alive is configured, when B comes up and A stays down, the server is
selected from C and D.