Getting the deep down muck on DDM!
DDM or Distributed Data Management has been around on IBM i since it was the good old AS/400 (probably even before that). Let’s get Deep Down into the Muck (DDM?) of DDM. What is it and why does iCluster need it? The DDM support on IBM i allows application programs or users to access data files that reside on remote systems, and also allows remote systems to access data files on the local IBM i system. iCluster is one of those applications that makes extensive use of DDM – mostly for accessing its own metadata files on a remote node. Some of the uses for DDM in iCluster include:
- Remote journal replication.
- WebSphere MQ replication.
- File activation of files that are in an out-of-sync (ACTOOS) state
- DMMONHA—replication monitoring.
- File content sync check.
- Status monitors in TR2
This list is not meant to be complete by any means, but gives you an idea as to how pervasive it is.
Most companies will have DDM access already configured, but just how secure that configuration is depends on the customer. Issue and prompt the CHGDDMTCPA command to see the level of DDM security configured for your shop. If the PWDRQD parameter as below is anything other than *USRID or *VLDONLY, you have secure DDM configured and iCluster will require its DMCLUSTER profile to be server authenticated (have a QDDMSERVER authentication entry) on every node in the cluster, to enable it to conform to the DDM security configured.
To create the QDDMSERVER authentication entry for the DMCLUSTER user profile, enter the following IBM i command on every node:
ADDSVRAUTE USRPRF(DMCLUSTER) SERVER(QDDMSERVER) USRID(<name>) PASSWORD(<password>)
<name> is the userid that exists on all nodes of the cluster
<password> is a valid password for the userid
If the password changes, use the Change Server Authentication Entry (CHGSVRAUTE) command to update the QDDMSERVER authentication entry. With these steps iCluster will be able to do all the stuff it needs to do, so if you are deep in the muck with some unexpected errors in replication, check these settings!