DBWRs and IO_SLAVES vs. Async IO

[wakedba]

We're using Oracle 10.2.0.4 on Solaris 10 with async turned on in the DB and async on in the OS. Our db_writers is set to 4, io_slaves is set to 0. We're noticing slow DBWR performance on our PROD server and much faster performance on our TEST server, both are the same systems, same patch level and same configurations for Oracle. I've recently seen some documentation that states you should use one or the other, if using async io set db_writers = 1 (and possibly io_slaves as well) otherwise if not using async io set db_writers = 4 and set io_slaves = 4 (or whatever recommended values based on CPU). Does anyone have any insight into this? We trying to determine why the DBWR is slow, LOG writer is fast, CPU isn't terribly busy, IO doesn't seem busy however we're getting GC alerts that say "Disk Device Busy (%)" at 98% sometimes but I can't find the command that GC uses to determine this in GC's documentation with all of the other alerts and their associated commands.

[mahajanakhil198]

This is from Oracle Docs. I hope it will help you.

DBWR_IO_SLAVES: This parameter is only relevant on systems with only one database writer process (DBW0). This parameter specifies the number of I/O slaves that is used by the DBW0 process. The DBW0 process and its slaves always write to disk. By default, the value is 0 and I/O slaves are not used.
If DBWR_IO_SLAVES is set to a nonzero value, the numbers of I/O slaves used by the ARCn process and LGWR process is set to 4. However, the number of I/O server processes used by Recovery Manager is set to 4 only if asynchronous I/O is disabled (either your platform does not support asynchronous I/O or DISK_ASYNCH_IO is set to false.
Typically, I/O slaves are used to simulate asynchronous I/O on platforms that do not support or implement it inefficiently. However, I/O slaves can be used even when asynchronous I/O is being used. In that case, the I/O slaves use asynchronous I/O.

[LKBrwn_DBA]

Try the FILESYSTEMIO_OPTIONS=SETALL parameter.

Here are some links to check:
http://www.solarisinternals.com/wiki...php/Direct_I/O
http://www.dba-oracle.com/oracle_tips_direct_io.htm
http://www.oracle-base.com/articles/...chronousIO.php