Re: Detecting xxx fragmentation/corruption?

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.

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Daniel Fink

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