Comtech EF Data VMS v3.12.x Vipersat - Manual (Page 415)

Appendix C - Redundancy C-5
MN/22156, rev 12 VMS Redundancy
Server Synchronization
Server synchronization is always executed by/from the active VMS server, and
is performed to ensure that all standby servers receive any necessary updates
due to changes in the master database that resides in the active server. Two
types of server synchronization occur with a redundant VMS configuration,
automatic and manual.
Automatic Synchronization
As the name implies, automatic synchronization occurs automatically by the
active VMS and is performed whenever any changes occur that are associated
with automatic system functions, such as automatic switching, device redun-
dancy, etc. The active server maintains a memory cache that holds the updates
until they can be pushed out to the standby servers by an automatic synchroniza-
tion that occurs during the VMS heartbeat. The updates are tagged onto the
heartbeat message that is sent by the active server to the standby servers.
Manual Synchronization
Manual synchronization, also referred to as “full synchronization”, must be
performed by administrator/user command for any changes not related to auto-
matic VMS functions, such as whenever any database configuration changes are
made to the server. Should a standby server be restarted, when it rejoins the
redundancy group, the sequence of updates may be lost and a manual synchroni-
zation is required to ensure that the standby receives the most current database
from the active server.
Note that this operation can be automated on a 24-hour basis with the Auto
Synchronize feature. See the section, “Auto Synchronize” on page C-9, for how
to configure this feature.
During a full synchronization, the active VMS service is temporarily taken
down to avoid any changes occurring during the synchronization process. The
active server sends the contents of the temp file holding the entire database
backup to each standby server via simultaneous unicasts. If, for any reason,
there is a failure with this update process, a notification will appear in the
windows log.
Server Contention
Server contention is a built-in protection mechanism for redundant VMS opera-
tion. A situation may occur where the active server briefly loses network
connectivity—a network cable is unintentionally pulled, for example—before
communications are restored. The first priority standby will become active due