When you have a CIFS preposition (PP) job set up to preposition a set of directories, and the same file exists in two directories at the same server, this is what you can expect: The file itself will be considered to be two separate files and will be cached separately in the CIFS cache. Requests through CIFS to read the data--to pull down and cache the file--will pass over the network separately for both of the files. In that sense, the file is being pulled across the WAN twice. However, because of DRE and LZ, the first pass also caches the data chunks in the DRE cache and zips what is sent over the wire the first time. Then, the second pass will actually transfer very, very little data. That second pass will almost all consist of DRE signatures that point to the data chunks already cached by DRE at both peer WAEs.
When you preposition a file in the CIFS cache, it is actually stored as a whole file in the CIFS cache and also as chunks of data bytes in the DRE cache. When you access the same file through another protocol, such as FTP or HTTP, the CIFS cache is not used. The CIFS cache is only used for CIFS requests. However, as you mentioned in your question, the DRE cache is used regardless of protocol or direction. So, subsequent requests for the same file using FTP, HTTP or some other protocol will pass DRE signatures instead of the raw data. Even though you won't see benefit from the CIFS cache, you will see benefit from both DRE and LZ.
By the way, Michael Holloway and I are currently hosting a WAAS Monitoring and Reporting discussion here:
https://supportforums.cisco.com/thread/2036888?tstart=0
If you have further questions related to monitoring and managing WAAS or a WAE, or collecting reporting information, we'd love to have your questions posted there.
