Good point to start: Tuning 'log file sync' wait events <http://orainternals.wordpress.com/2008/07/07/tuning-log-file-sync-wait- events/> Thanks, Timur Akhmadeev ________________________________ From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Crisler, Jon Sent: Tuesday, April 07, 2009 8:17 PM To: oracle-l@xxxxxxxxxxxxx Subject: Mirroring redo log groups or not ? I am dealing with a possible performance issue with "redo log sync wait". This is for 10g 10.2.0.4 on Linux 64. In troubleshooting this problem, one of the things I did was to cut down the redo logs so that there is only 1 member per group rather than 2 (i.e. redo log mirroring). Each member goes to a different LUN, and the LUN's are Raid-5. Here is the layout- LUN 1 is 1 TB approx, Raid-5 used for database files LUN 2 is 500 gb Raid 5 used for RMAN backups to disk, LUN 3 is 500 gb Raid 5 used for archive log destination All are SAN connected via 2 - 4gb Qlogic HBA's with multipath. Now, currently online redo logs are going to Lun 2 for the first member and Lun 3 for the second. So there is going to be a little bit of contention when archiving, but whichever LUN I point to is going to encountered contention. It would be very difficult to add more LUN's due to SAN restrictions, but I have the option of converting either LUN 2 or 3 to Raid 1 / 0. If I converted to Raid 1/0 I could point one or both members to this LUN. There appears to be some performance difference with our hardware between Raid 1 and Raid 5, but not a great deal in actual testing. So, if the LUN that holds the online redo logs is already protected (raid 1, 5 etc) do I really need to mirror the online redo logs ? Should I convert the LUN to Raid 1 / 0 ? if I convert to Raid 1/ 0 should I keep redo log mirroring and point to the same LUN ? The information transmitted herein is intended only for the person or entity to which it is addressed and may contain confidential, proprietary and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any computer.