RE: Mirroring redo log groups or not ?
Date: Wed, 8 Apr 2009 11:56:34 +0400
Message-ID: <17182849A17B3C44AE01780E7B519C8202660917_at_WISE.netcracker.com>
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_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Crisler, Jon
Sent: Tuesday, April 07, 2009 8:17 PM
To: oracle-l_at_freelists.org
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 ?
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