Re: Detecting xxx fragmentation/corruption?

From: Daniel Fink <>
Date: Fri, 09 May 2008 19:55:05 -0600
Message-ID: <>

To supplement Jared's response... Inline

Peter Teoh wrote:
> Unlike memory, where access time almost zero, accessing the disk is
> much slower. So sometimes I thought it will be better to spread out
> the data - thus enable simultaneous read by the different heads in the
> disk, just like those RAID design. Ie, fragmentation via
> distribution the blocks out in the disk can improve performance - can
> such things happened?

In terms of reading data in memory, access time may be almost zero, but the time required to read a block in memory is not thousands of times faster than reading it from disk. I don't recall the exact figure from a Cary Millsap presentation ("Why You Should Focus on LIOs"?)some years ago, but the difference was something like 42 times. If you add in time required to create a read consistent version, a single logical i/o could take much more time than a physical i/o.

Daniel Fink

Oracle Performance, Diagnosis, Data Recovery and Training

Oracle Blog

Lost Data?

Received on Fri May 09 2008 - 20:55:05 CDT

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