Oracle Database Discussions

Hi,
Oracle Database 11g Release 11.1.0.6.0 - 64bit Production With the Real Application Clusters option.

After I noticed this error into the alert log:

Thread 2 cannot allocate new log, sequence 152831
Checkpoint not complete
Current log# 17 seq# 152830 mem# 0: +ONLINELOG/evodb/onlinelog/group_17.272.729333887
Thread 2 advanced to log sequence 152831
Current log# 14 seq# 152831 mem# 0: +ONLINELOG/evodb/onlinelog/group_14.269.729333871

And read a lot to understand the real cause (for the moment I increased the the redolog file from 5 to 7 (250mb each)).

As it seems I've no problem with the ARCH processes, I read that the cause can be the DBWR0 process that is not "fast" enough to write block I've into redos, and free them for archiving.

I read then something about the asynchronous I/O, and how db_writer_processes/dbwr_io_slaves can simulate the async write to disk.

I think I understood the difference between db_writer_processes and dbwr_io_slaves.
My question is how I can understand if my database needs more DBWR process.

At the moment my configuration is:

db_writer_processes 1
dbwr_io_slaves 0

Thanks in advance,
Samuel