Excessive IOPS to shared ORACLE_HOME

From: Chen Shapira <cshapi_at_gmail.com>
Date: Thu, 21 Aug 2008 19:45:16 -0700
Message-ID: <e37540930808211945h6944efd3q3795d35feb360dfc@mail.gmail.com>

Hi Oracle Fans,

I need some help and advice on tracking down source of excessive IO.

Our 10.2.0.[2,3] RAC enviroments are configured with shared ORACLE_HOME, residing on Netapp storage. The same volume also contains the voting disk and OCR for the RAC.
This volume, that we assumed will have almost no load, actually has about 6000 IOPS (IO operations per second), sometimes up to 13000. For comparison, our data volume has about 1500 IOPS.

Interesting findings:
1) From Netapp reports and from some network sniffing, it appears that over 90% of the IO is "access" and "get attribute" operations - neither reads, nor writes.
2) This does not happen to the voting disks on RAC systems that have no shared home. (although there are other configuration differences as well).
3) This also does not happen in stand alone systems that have ORACLE_HOME on the Netapp.

I can't use IOSTAT to debug because it does not report NFS. Network monitoring aggregates over all NFS traffic, so I can't seperate normal data traffic from strange ORACLE_HOME traffic (it is all on same storage interface). Linux does not report network activity per process (not without special patches). Wait event tables will not show traffic to Oracle_home or to voting disk.

Any suggestions where to look?
Anyone can guess what we could have configured wrong to cause such an issue? ( I know that we are all against random guessing, but it feels like all investigation channels are insufficient).

Chen Shapira

Received on Thu Aug 21 2008 - 21:45:16 CDT

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