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> Multiplexing redo logs and control files to a separate diskgroup in ASM, General question this one...
RupertMerkin
post Mar 1 2011, 06:24 AM
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I've been using ASM for a few years now and have always installed a new system with 3 diskgroups

+DATA - for datafiles, control files, redo logs
+FRA - for achive logs, flash recovery. RMAN backup

Those I guess are the standards, but I've always created an extra (very small) diskgroup, called +ONLINE where I keep multiplexed copies of the redo logs and control files.

My reasoning behind this is that if there are any issues with the +DATA diskgroup, the redo logs and control files can still be accessed.

In the olden days (all those 5 years ago!), on local storage, this was important, but is it still important now? With all the striping and mirroring going on (both at ASM and RAID level), am I just being overtly paranoid? Does this additional +ONLINE diskgroup actually hamper performance? (with dual write overheads that are not necessary)

Thoughts?

Rup
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Kamran Agayev A.
post Mar 1 2011, 06:26 AM
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I'd suggest you to NOT rely on hardware mirroring and try multiplexing your online redo log files


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Kamran Agayev A.
Oracle ACE and Oracle Certified Professional 9i,10g
Author of "Oracle Backup & Recovery: Expert secrets for using RMAN and Data Pump"
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RupertMerkin
post Mar 1 2011, 09:30 AM
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In which case you think my reasoning is sound...?
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SteveC
post Mar 1 2011, 12:46 PM
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And when there are problems with NAS, you have the opposite problem. Put them on both and be done with it.

http://dbaforums.org/oracle/index.php?showtopic=20591
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burleson
post Mar 8 2011, 09:50 AM
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H Rupert,

>> is it still important now?

Yes! You never want a single point of failure, even with a mirrored ASM file . .

I have clients that triple mirror all data files!

There are no "rules" that says you cannot multiplex "vanilla" redo logs, and manually place them on physical disk spindles that also contain ASM files!

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>> I've always created an extra (very small) diskgroup, called +ONLINE where I keep multiplexed copies of the redo logs and control files.

That's fine. Oracle says it's OK to multiplex redo logs in ASM:

http://dba-oracle.com/googlesearchsite_pro...exing+redo+logs

Of course, one drawback is that ASM is raw, and ASM redo log files are NOT on OS JFS filesystems.

Good Luck!


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Donald K. Burleson
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