BIG IP DNS synchronization

Hi everyone,

When we have a two BIG IP DNS devices in site a and need to perform synchronization between them what are the needed configuration,

1-Is HA between devices matter should be configured ?! devices have DNS provision no LTM nor ASM

2-From new DNS device we will perform gtm_add <existing DNS device IP> and this will replace GTM configuration on new appliance with configuration existing on DNS device also exchange certificates, anything else required ?

3-What about if we create a zone record, datacenter will that be synced ?!

4-in case of configuration under GSLB like datacenter and servers, we have to enable synchronization under settings GSLB and thats it ? or have to add current BIGIP and other one as servers first ?!

5-what exactly meant by 

5-According to zone synchronization it is not related to configuration sync under GSLB and will by synced by define a slave zone ?!

6-I notice when making normal HA configuration like in LTM zone synced from first DNS appliance to second one