Re: Disk geommetry, was Re: Kernel Upgrade: Why?
> Think of it as a record (ya' know those old odd looking vinyl things).
> It spins at 33.3 rpm but the sound/music doesn't change from outer to inner.
> Same deal with hard drives although the outside is 'spinning' faster, it
> still picks up the same amount of data per rotation as it would near
> the center.
I don't think this is true.
This is a part from
http://www.quantum.com/src/storage_basics/c3.5_part2.html#geometry
In earlier hard drive designs, the number of sectors per track was
fixed and, because the outer
tracks on a platter have a larger circumference than the inner tracks,
space on the outer tracks
was wasted. The number of sectors that would fit on the innermost
track constrained the
number of sectors per track for the entire platter. However, many of
today's advanced drives
use a formatting technique called Multiple Zone Recording to pack
more data onto the surface
of the disk. Multiple Zone Recording allows the number of sectors
per track to be adjusted so
more sectors are stored on the larger, outer tracks. By dividing
the outer tracks into more
sectors, data can be packed uniformly throughout the surface of a
platter, disk surface is used
more efficiently, and higher capacities can be achieved with fewer
platters. The number of
sectors per track on a typical 3.5-inch disk ranges from 60 to 120
under a Multiple Zone
Recording scheme. Not only is effective storage capacity increased by
as much as 25 percent
with Multiple Zone Recording, but the disk-to-buffer transfer rate
also is boosted. With more
bytes per track, data in the outer zones is read at a faster rate.
Quantum Corporation is a
pioneer in Multiple Zone Recording, and was the first manufacturer
to implement Multiple Zone
Recording on 2.5-inch disk drive products.
Groetjes, Ookhoi
> > -----Original Message-----
> > From: Richard Harran [SMTP:95rmwh@eng.cam.ac.uk]
> > Sent: Friday, April 23, 1999 8:35 PM
> > To: Jonathan Guthrie
> > Subject: Re: Disk geommetry, was Re: Kernel Upgrade: Why?
> >
> > I think that you are missing a very important point here. A hard disk,
> > unlike, for example, an audio CD-ROM, spins at a fixed angular
> > velocity. Thus the 'linear' speed over the disk surface is faster
> > towards the outside of the disk than towards the centre (as in v=wr).
> > Thus at the
> > very least, it would seem likely that the reading of a large amount of
> > data which was continuous would be quicker from the outside of the disk
> > than from the innner. (This probably represents a larger performance
> > increase with the large web-server than with the average single-user
> > system).
> >
> > That said, I take your point about the seek time depending on the
> > distance that the heads have to move, and it is evident that multihead
> > drives would be expected to improve performance.
> >
> > Rich
> >
> > Jonathan Guthrie wrote:
> > >
> > > On Thu, 22 Apr 1999, Ookhoi wrote:
> > >
> > > > Well, there was a discussion here about a benchmark Linux vs NT, and
> > > > some people here said that the preformance of Linux could have been
> > > > affected by the fact that Linux was near the center, and NT on the
> > outer
> > > > side.
> > >
> > > Probably not the reason.
> > >
> > > > And the data on the outer side passes the heads much faster than the
> > > > data on the inner side. But then, there is much more data on the outer
> > > > side, and a piece of data on the outer side will go round in the same
> > > > amount of time as a piece of data on the inner side..
> > >
> > > I am not aware of any disks that use a higher density recording format
> > for
> > > the outer tracks than they do for the inner tracks. As far as I am
> > aware
> > > (and I really haven't paid much attention to such things since ST-277's
> > > were state of the art) the bit density of the outer tracks is LOWER than
> > > the bit density of the inner tracks. That's because the outer tracks
> > are
> > > physically larger, but they hold the same number of bits.
> > >
> > > Not that it matters. The whole disk spins as a single unit so even if
> > > there were more bits on the outer tracks, you'll still wait the same
> > > amount of time (on average) for the sector you want to come around.
> > Read
> > > on, and I'll explain.
> > >
> > > > So, is there an advantage if whe put for example swap at the outer
> > side
> > > > of a disk?
> > >
> > > NO!
> > >
> > > Look, the access times for disk are dominated by two times, the time to
> > > seek to the correct track and the time to wait for the data to come
> > around
> > > again on the disk. The time it takes the data to come around on the
> > disk
> > > is, on average, one half of the time it takes for the disk to go around
> > > once. That's independant of everything else and is a fairly short time,
> > > anyway.
> > >
> > > The time it takes to seek to the correct track depends upon where you're
> > > seeking from and where you're seeking to. Obviously, if the heads
> > happen
> > > to be at innermost cylinder, it will take longer to seek to the
> > outermost
> > > cylinder than if the heads were in the middle or toward the outside.
> > So,
> > > for higher performance in a situation where you're too cheap to add
> > enough
> > > RAM, you'll want the swap file near where the heads are likely to be.
> > >
> > > You can also turn that around. Seeking to the middle from either
> > extreme
> > > is likely to be faster than seeking to the other extreme. (This works
> > for
> > > both average and worst-case times.)
> > >
> > > Predicting where the heads are likely to be takes some doing, especially
> > > on systems with effective disk caches, but you can take some educated
> > > guesses. The middle of a disk is a better guess than either extreme,
> > but
> > > isn't necessarily the best guess. If you spend a lot of time reading
> > and
> > > writing (especially writing) files from a particular partition, you
> > might
> > > want to put the swap file near that partition on the principle that the
> > > heads are likely to be near there anyway, so it should reduce the amount
> > > of time waiting for any given swap.
> > >
> > > An extreme example of this would be where you dedicate an entire drive
> > to
> > > a (fairly small) swap partition. That's how the news servers I use do
> > it.
> > > For something less extreme, I kind of like the recommendation made by
> > OS/2
> > > gurus: Their advice was to put the swap file in the most used partition
> > > on the least used drive. You might try something like that where you
> > put
> > > the swap partition in the middle of a disk that isn't used for very
> > much.
> > >
> > > In short, my recommendation for boosting the performance of a computer
> > > that uses a significant amount of swap is to add RAM to the computer.
> > >
> > > HTH. HAND.
> > > --
> > > Jonathan Guthrie (jguthrie@brokersys.com)
> > > Brokersys +281-895-8101 http://www.brokersys.com/
> > > 12703 Veterans Memorial #106, Houston, TX 77014, USA
> > >
> > > --
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> >
> >
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>
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