Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 108)

92 Brocade Virtual ADX Server Load Balancing Guide
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Hash-based SLB with server persistence
2
Real server failure
If a real server fails, the Brocade Virtual ADX will remove all assignments of the real server from all
persistent hash table entries in the persistent hash table.
For example, consider a virtual server vs1 whose port HTTP is bound to port HTTP of real server rs1
and rs2.
Figure 18 shows the persistent hash table for vs1 for port HTTP before server failure.
FIGURE 18 Hash table before server failure
Real server rs1 has been assigned to persistent hash table entries corresponding to hash value 0
and hash value 2. Real server rs2 has been assigned to the entry corresponding to hash value 1.
Now assume all other hash table entries have not been assigned to any real servers.
If port HTTP of real server rs1 fails, then the Brocade Virtual ADX will clear assignment of rs1 to the
persistent hash entries in the above table.
Figure 19 shows the persistent hash table for vs1 for
port HTTP after server failure.
FIGURE 19 Hash table after server failure
The Brocade Virtual ADX does not immediately assign a new server to the cleared hash table
entries. Instead, the Brocade Virtual ADX will select and assign a real server for these entries using
the SLB predictor the next time a client hashes to these hash table entries.
virtual server vs1 port http
Hash 0
Hash 1
Hash 2
Hash 255 none
rs2
..............
Persistent Hash table
rs1
rs1
virtual server vs1 port http
Hash 0
Hash 1
Hash 2
Hash 255 none
rs2
..............
Persistent Hash table
none
none