There are two aspects of write bitmaps that affect performance;
the message traffic that occurs between local and master write bitmaps
and the size requirements of each bitmap.
The message traffic can be adjusted by changing the message
mode. Single message mode is the default. Buffered message mode
can improve overall system performance, but the time to record each
process's write in the master write bitmap usually takes longer.
These modes are described in detail in
System Parameters for Managing Write Bitmap Messages and Shadow Set Limit.
Additional memory is required to support write bitmaps, as
described in
Memory Requirements. Depending
on the memory usage of your system, it may require additional memory.