If you have proven that the cause of the slow performance is due to higher-than-acceptable I/O latency within the Oracle database, and you have determined that this condition isn't happening in other Oracle databases which are not Delphix VDBs, and if you have proven that the problem is not due to inadequate UNIX/Linux kernel parameter settings for NFS, and you have proven that the problem is not due to inadequate network latency and/or throughput, then it is reasonable to look within the Delphix Virtualization Engine for possible contention or bottlenecks to performance.
The Performance Analytics capability of the Delphix Virtualization Engine displays utilization of the compute, network, and storage resources allocated. Connecting into the administrative console of the Delphix Virtualization Engine and then navigating to Resources > Performance Analytics will display information about CPU, Network, Disk I/O, NFS, andiSCSI. The last resource (iSCSI) pertains to Windows platforms running MSSQL only, but the other four resources (i.e. CPU, Network, Disk I/O, and NFS) should be analyzed with Oracle VDBs running on UNIX/Linux platforms.
The Performance Analytics graphical user-interface is capable of displaying all five resources at once, but that makes for a busy display and it is highly recommended to examine one resource at a time. As you view the information on your Delphix Virtualization Engine, please refer to the online documentation to understand and interpret the displayed information...