RE: Performance tuning

From: Christopher Spence <cspence_at_FuelSpot.com>
Date: Wed, 30 May 2001 10:30:50 -0700
Message-ID: <F001.00313E01.20010530100214@fatcity.com>

Raid 5 can consume as much as 60% overhead for writes.

"Walking on water and developing software from a specification are easy if both are frozen."

Christopher R. Spence
Oracle DBA
Fuelspot

-----Original Message-----

Sent: Wednesday, May 30, 2001 12:51 PM
To: Multiple recipients of list ORACLE-L

John, have you read Cary Millsap's paper on RAID 5? www.hotsos.com I believe. RAID 5 will require additional writes by DBWR which is going to be huge overhead during a dataload.

Ethan Post

-----Original Message-----

Sent: Wednesday, May 30, 2001 6:51 AM
To: Multiple recipients of list ORACLE-L

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Peter McLarty wrote
"Are you running RAID and if so what configuration. (Not RAID 5 I hope)"

Interesting. I am posting an excerpt from Doc 97597.1 Optimising Raid performance for Oracle RDBMS on NT

RAID 5 is useful for Oracle datafiles but not for redo log files or rollback segments which are sequentially accessed. Datafiles belonging to the temporary tablespace are not suitable for a RAID 5 device. More benefits will be seen in situations where reads predominate over writes.

I know that in this instance it is a data load that is being discussed but presumably once the data is loaded then it will be read more than once.

Certainly the tone of the note suggests that raid 5 is not a definite no-no rather a 'be cautious as to which files are placed where'. It is my belief that often a single raid level is set for all files rather than a mix of raid 1 and raid 5 as appropriate.

Peter, I fully agree that the level of memory utilised here is totally insufficient and is very likely to be the constraining factor in this case.

John

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Author: Post, Ethan
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Author: Christopher Spence
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