File Copy Based Initial Sync currently changes storageGlobalParams.dbPath while holding a global X lock. This parameter is normally read without locking, so it can be read while it is being written resulting in a data race. We should fix this, either by

1) Having FCBIS not change storageGlobalParams.dbPath

2) Outside server startup, requiring any global lock to be held while accessing storageGlobalParams.dbPath and formalizing that with an accessor requiring an opCtx.

3) Locking around it specifically or making it a pointer and using an atomic swap to set it.