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Re: I/O Optimization

At 11:57 AM -0800 1/27/01, David A. Gatwood wrote:

With modern hard drives, there is no way to really know
the track numbers associated with block numbers. You can assume that
closely numbered sectors are near others, but increasing block numbers
could move the arm from the inside of the disk to the outside (nad
possibly vice-versa) several times.

Why would this ever happen? Think about it a little more before you assume it's a possibility worth worrying about. Such behavior would destroy streaming read/write throughput for large files.

General purpose file systems designed for hard disks *all* know in their bones that laying out a large file with monotonically increasing block numbers, and few (if any) discontinuities, is the One True Path to high streaming throughput.

Hard drive vendors know about this, and those who want to keep their customers take care to avoid violating such simple (and eminently reasonable) expectations.

I hope that we have now plumbed the depths of thinking about hardware devices from too abstract a POV... (in other words, one shouldn't assume that because something *could* happen that it *will*; it's important to think about what's actually likely to happen...)

Tim Seufert

References: 
 >Re: I/O Optimization (From: "David A. Gatwood" <email@hidden>)



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