[standalone@localhost:9990 /] /subsystem=io/buffer-pool=foo:write-attribute(name=buffer-size, value=-20
{
    "outcome" => "success",
    "response-headers" => {
        "operation-requires-reload" => true,
        "process-state" => "reload-required"
    }
}

2017-02-27 08:36:29,222 ERROR [org.jboss.as.controller.management-operation] (Controller Boot Thread) WFLYCTL0013: Operation ("add") failed - address: ([
    ("subsystem" => "io"),
    ("buffer-pool" => "foo")
]) - failure description: {
    "WFLYCTL0080: Failed services" => {"org.wildfly.io.buffer-pool.foo" => "org.jboss.msc.service.StartException in service org.wildfly.io.buffer-pool.foo: Failed to start service
    Caused by: java.lang.IllegalArgumentException: XNIO000015: Parameter 'bufferSize' is out of range"},
    "WFLYCTL0412: Required services that are not installed:" => ["org.wildfly.io.buffer-pool.foo"]
}