Things are not always what they appear to be.
In Vista and later the "Cached" value in Task Manager does not refer to the disk cache, neither does it include it. Nothing in Task Manager will show the size of the disk cache. I believe the only system supplied utility that will is the Performance Monitor. With typical desktop usage the disk cache will be much smaller than the "Cached" value. In a heavily used server it will be larger. The size and contents of the disk cache is under the control of the system memory manager. If it is large it is because it is being used a lot.
The "Cached" value is the sum of the Standby list and the Modified list. You can see these values in Resource Monitor. The Standby list contains memory from executable files that are not currently being used, memory trimmed from applications, and more. It may contain data that was trimmed from the disk cache. In most cases the Standby list will form the largest portion of "Available" memory. The contents of this memory is still available to the application that previously owned it if it is needed. A large value is a good thing.
The Modified list consists of memory trimmed from process working sets and waiting to be written to the pagefile, after which it will go to the Standby list. Typically it will be quite small. Like memory on the Standby list this data can be reclaimed by an application if needed
I am not aware of any way to prevent write caching. If you are having a problem it needs to be investigated. Disabling a normal system process is not usually a viable solution to a problem.