And they are no longer "cyl groups", but they are block groups.
Assuming a 1k block size, the block groups are 8Mb. No attempt is
made to align them to cylinder boundaries.
> > not useful anymore. With modern disks, chances are excellent that the
> > specific 3D geometry the file system sees is an utter fiction, and
> > that cylinder locality is thus more-or-less a meaningless concept.
>
> If it was meaningless then things like sorting write queues would also
> be pointless. Its certainly true that the 3D information is less than
> useful nowdays. Its not however true that relative distance (in time)
> between sectors is not strongly proportional to the difference in sector
> numbers, or that reading sectors is order of sequentional logical number
> isnt a good thing
REW: E-too-many-negatives: Brain overflow.
Reading a block that is 2 blocks away from the last block you read
will just take (2 blocks / raw_disk_speed). That's very proportional
to the difference in sector numbers. But it is a "law" that only
holds for "small" values of the difference. (It holds upto about
10ms: the time it takes for a full rotation)
So, once you leave the current track, you're usually facing a seek
time (or head-switch-time (*)) of about 3ms, plus the average rotational
latency of about 5ms. A "long distance" seek is not that much worse:
as a disk claims an average seek time of 8 or 10 ms, which is only
about three times the track-to-track seek time.
Roger.
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