Solution for persistence

Create four pools, designating one of your servers as priority in each, cascading down respectively:

pool1 pool2 pool3 pool4

1.1.1.1:80 pri 40 1.1.1.2:80 pri 40 1.1.1.3:80 pri 40 1.1.1.4:80 pri 40

1.1.1.2:80 pri 30 1.1.1.3:80 pri 30 1.1.1.4:80 pri 30 1.1.1.1:80 pri 30

1.1.1.3:80 pri 20 1.1.1.4:80 pri 20 1.1.1.1:80 pri 20 1.1.1.2:80 pri 20

1.1.1.4:80 pri 10 1.1.1.1:80 pri 10 1.1.1.2:80 pri 10 1.1.1.3:80 pri 10

Then, it's a simple irule:

when CLIENT_ACCEPTED {
  switch [IP::remote_addr] {
    "src_ip_S1" { pool pool1 }
    "src_ip_S2" { pool pool2 }
    "src_ip_S3" { pool pool3 }
    "src_ip_S4" { pool pool4 }
    default { pool default }
  }
}

Makes sure your servers will always go to the right member as long as it's up, but will survive outages as well. HTH...Jason