Hi,
I'll try to answer your questions here:
Q1 - The compression is implemented by the Delphix filesystem internally when data is written to it, it is totally transparent to whatever reads/writes it (usually a Database instance). Delphix essentially takes a 'copy' of the source database and keeps this (compressed) copy on Delphix storage.
Q2 - A VDB's data is not stored on a target server, it is mounted over the network from the Delphix Server. However, to the target server, it will look the same size as the source.
Q3 - As above, the compression is not visible to the database. It just means less disk space is used by Delphix.
Q4 - As above, it does not use any space on the target machine. The space is used on Delphix.
To clarify, Delphix does not store
any database data on a target server, only internally on the Delphix server itself. The only space used on a target system by Delphix is for what we call the "toolkit", which is basically the small set of tools we need to mount/unmount filesystems, start/stop the VDBs, and similar tasks.
I hope that helps,
Scott.