topic Re: Different IO STAT Figures in Operating System - Linux

Different IO STAT Figures

faisal chaudry — Wed, 13 Apr 2011 09:57:54 GMT

MSAP2000 is connected to 2 DL380G7 Servers.

There are 16 logical volumes on MSA & all volumes are appeared on both DL380 Servers.

When IO Stat is run on both servers at the same time then both servers shows output with different IO Stats figures means one server is generating too much IOs on same SAN Disks on which other server is not generating that much IOs.

Both servers are part of ORACLE RAC.

Can anybody help that is it a normal behavior OR not ?

Re: Different IO STAT Figures

Reiner Rottmann — Wed, 13 Apr 2011 18:28:57 GMT

Oracle RAC allows parallel access to the database. In order to achieve that, the application uses a sophisticated locking mechanism. If two nodes try to access the same data with read/write access, they must negotiate that the section of the database is consistient. One server has to stop writing to the section and the other node may continue using that data. Naturally that means that sections that are solely used by a single node may be accessed faster and those SAN disks are stressed more.

Re: Different IO STAT Figures

faisal chaudry — Thu, 14 Apr 2011 03:50:45 GMT

Hi Reiner,

Thanks for the reply.

Can you please help to clarify one point that if Node-1 is writing on same SAN Disk on which Node-2 is not writing then if IO STAT is run on both Nodes, why both nodes show different IO STAT figure.

What I mean to say is this that why Node-2 is showing less IO STAT figures when actually its not writing on that specific SAN Disk at all which is in use of Node-1 for data writing.

Re: Different IO STAT Figures

faisal chaudry — Fri, 15 Apr 2011 07:45:44 GMT

Hi,

I hope I am able to clarify the issue,

Either Node-2 should show zero IOs or should show the same number of IOs which are being generated by Node-1 during
Data Writing.

I am also working with Oracle Support Team for this behavior but they are still working on it need some more time to find the exact reason of this behavior of Node-2.

Thanks,