Technical data

Brocade ServerIron ADX Advanced Server Load Balancing Guide 61

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Other transparent cache switching options

Consider an example where there are 64 cache servers within one cache group (CS1 through

CS64). Because there are 256 buckets, each server is assigned four buckets (256 / 64 = 4). If one

cache server (CS1), goes down, the four buckets assigned to CS1 are re-assigned to cache servers

“CS2-CS5”. Consequently, “CS2-CS5” have five buckets each while CS6 through CS64 still have

four buckets. This means that the original traffic handled by the cache server going down is not

distributed evenly among the rest of the cache servers. The traffic on CS2 through CS5 increases

by 25 percent ([ 5 - 4] / 4= 25%).

You can increase the TCS hash bucket count to a higher number to ensure a more reasonable

distribution of excess traffic among remaining cache servers when a cache server goes down.

Using the previous example in which there are 64 cache servers(CS1-CS64) you can upgrade the

TCS hash bucket count to 8192. Because 8192 / 64 = 128, each server is now assigned 128

buckets. If one cache server (CS1) goes down, then the 128 buckets assigned to CS1 are

re-assigned to the other 63 servers. In this situation, CS2 and CS3 get three additional buckets

each while CS4 through CS64 get two buckets each ([2 * 3] + [61 * 2] = 128). The result is that the

original traffic handled by the cache server that went down is now distributed evenly among the

remaining functional cache servers. The traffic on CS2 and CS3 increases by 2.34 percent ([131 -

128] / 128 = 2.34%), and by 1.56 percent on CS4 through S64 ([ 130 - 128] / 128 = 1.56%).

Configuring an increased hash bucket count

You can set the size of the TCS hash bucket count to a value from 256 through 16384 using the

system-max command.

ServerIronADX(config)#system-max tcs-hash-table-size 2048

Syntax: [no] system-max tcs-hash-table-size hash-table-size

The hash-table-size variable specifies the size that you want to configure the hash table.

Acceptable values are 256, 512, 1024, 2048, 4096, 8192, and 16384. Entering a value for this

variable other than an acceptable value will cause an error message to be displayed. The default

value is 256.

NOTE

The hash table size will only be effective after saving the configuration using the write mem

command and reloading the ServerIron ADX.