[TUHS] /dev/drum

Warner Losh imp at bsdimp.com
Tue Apr 24 08:15:05 AEST 2018

On Mon, Apr 23, 2018 at 4:07 PM, Tim Bradshaw <tfb at tfeb.org> wrote:

> On 23 Apr 2018, at 21:47, Grant Taylor via TUHS <tuhs at minnie.tuhs.org>
> wrote:
> > I had always wondered where Solaris (SunOS) got it's use of the
> different slices, including the slice that was the entire disk from.
> >
> > Now I'm guessing Solaris got it from SunOS which got it from 4.x BSD.
> >
> There is a wonderful Sun cretinism about this. At some recent time (I am
> not sure how recent but probably mid 2000s), someone worked out that you
> wanted swap to be at one end of the disk (I think the outside) because on
> modern disks the data rate changes across the disk and you wanted it at the
> end with the highest data rate.  But lots of things knew that swap was on
> s1, the second partition.  So they changed the default installation tool so
> the slices of the disk were out of order: s1 was the first, s0 the second,
> s2 was the whole disk (which it already was) and so on.  This was
> enormously entertaining in a bad way if you made the normal assumption that
> the slices were in order.  There was also (either then or before) some
> magic needed such that swapping never touched the first n blocks of the
> disk where the label and boot blocks were, and it was possible to get this
> wrong so the machine would happily boot, run but would then fail to boot
> again, usually at a most inconvenient time.
> And the cretinism was that this was mid 2000s:  if you had machine that
> was paging the answer was to buy more memory not to arrange for faster swap
> space: it was solving a problem that nobody had any more.

It's weird. These days lower LBAs perform better on spinning drives. We're
seeing about 1.5x better performance on the first 30% of a drive than on
the last 30%, at least for read speeds for video streaming....

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