Steve,
The OPAMSVDB is global variable database and has nothing to do with SYSPLEX variables.
OPSVARSRV uses the common services component CAVARSRV to create SYSPLEX variables. CAVARSRV stores the SYSPLEX variables in it's memory. Each CAVARSRV in the SYSPLEX synchonizes via the coupling facility. If a system goes down and comes back into the SYSPLEX it gets a copy of the variables from another CAVARSRV. This does not require the use of DASD. When using OPSVASRV to create or update SYSPLEX Variables. GLVPLTXTx variables are temporary in nature as they are available as long as one CAVARSRV is still running in the SYSPLEX. If the SYSPLEX goes down then these variables are not recoverable. GLVPLTXPx variables are considered permanent and are written to a “Shared” vsam file. If the SYSPLEX goes down the first CAVARSRV active reads the variables from this file. So If you do not have a requirement to keep the variables in case of a SYSPLEX outage then DASD is not required.
I hope this answers your question. If not please provide more detail about what you are trying to accomplish.