Hi Lukas,
WAAS solution is for optimization and latency mitigation for WAN links. Generally 8-10 msec latency
considerd to be very low for wide area networks.
For your original question, WRITE operation is usually slower than the READ operation mostly due to the nature
of the CIFS protocol itself rather WAAS.Let's say a user edits a file and makes a change to a it, and write it back, that operation
will require a full write over the WAN. A MS application is going to initially write
the changed file as a temporary file and then to original file name before sending it out.
The write operation is going to be slower than pulling from cache, because the file will
have to cross the WAN and will be subject to latency.
However, it will be much faster than a non-WAAS write operation because
you have optimization (TFO+DRE+LZ) as well as CIFS AO handling locally some of the
chattiness of CIFS.
On the write operation, we don't have the benefit of read-ahead, nor the
benefit of serving cache locally. We are writing as fast as the client can
gives us data and it can be sent over the WAN, while buffering to speed
up what the client gives us. The bits still have to be sent over the
WAN so the file server can store the new file. No way around that. But
We can get benefit of TFO/DRE/LZ.
Bottom line, READ and WRITE operations will not be equally comparable.
This link might help to understand some CIFS semantics:
http://www.cisco.com/en/US/docs/app_ntwk_services/waas/waas/v421/configuration/guide/filesvr.html#wp1042382
Hope this helps
Ashfaq-
