Here's some info I was able to dig up!
Ed Haskins
Oracle DBA
Verizon Wireless
Zoned Bit Recording
One way that capacity and speed have been improved on hard disks over time
is by improving the utilization of the larger, outer tracks of the disk. The
first hard disks were rather primitive affairs and their controllers
couldn't handle complicated arrangements that changed between tracks. As a
result, every track had the same number of sectors. The standard for the
first hard disks was 17 sectors per track.
Of course, the tracks are concentric circles, and the ones on the outside of
the platter are much larger than the ones on the inside--typically double
the circumference or more. Since there is a constraint on how tight the
inner circles can be packed with bits, they were packed as tight as was
practically possible given the state of technology, and then the outer
circles were set to use the same number of sectors by reducing their bit
density. This means that the outer tracks were greatly underutilized,
because in theory they could hold many more sectors given the same linear
bit density limitations.
To eliminate this wasted space, modern hard disks employ a technique called
zoned bit recording (ZBR), also sometimes called multiple zone recording or
even just zone recording. With this technique, tracks are grouped into zones
based on their distance from the center of the disk, and each zone is
assigned a number of sectors per track. As you move from the innermost part
of the disk to the outer edge, you move through different zones, each
containing more sectors per track than the one before. This allows for more
efficient use of the larger tracks on the outside of the disk.
More (http://www.pcguide.com/ref/hdd/geom/tracksZBR-c.html)
----------------------------------------------------------------------
Placing Data at the Beginning of ZBR Disks
Data is most quickly transferred when it is located at the beginning of
zone-based recording (ZBR) disks. Placing data at the beginning of these
disks improves the bandwidth for sequential data transfers.
-----------------------------------------------------------------------
Disk geometry refers to how sectors and tracks are organized for each
cylinder in a disk drive. The UFS organizes itself to use disk geometry
efficiently. If slices in a concatenated metadevice have different disk
geometries, DiskSuite uses the geometry of the first slice. This fact may
decrease the UFS file system efficiency.
Note - Disk geometry differences do not matter with disks that use Zone Bit
Recording (ZBR), because the amount of data on any given cylinder varies
with the distance from the spindle. Most disks now use ZBR.
------------------------------------------------------------------------
Use Outer Disk Cylinders First
Because of the Zone Bit Recording (ZBR) technology used by Sun, outer
cylinders tend to outperform inner cylinders. The outer cylinders are
cylinders 0, 1, and 3, as opposed to 4, 5, 6, and 7.
CAUTION: Remember, don't use cylinder 2, the overlap cylinder, because it
retains the total size of the disk. Some programs are baffled when this
cylinder gets changed.
-----Original Message-----
Sent: Tuesday, April 24, 2001 10:51 AM
To: Multiple recipients of list ORACLE-L
----- Original Message -----
> Ever since ZBR, the need to use the outside of the disk ( to
> reduce seeks ) is significantly reduced.
>
PMFJI.
The reason for using the outside of the disk is the increased
linear velocity there re the heads. Larger circle, same angular
velocity, larger linear velocity. Which means you get faster
read data transfer rate. Nothing at all to do with reducing
seeks. What you end up with is less rotational latency and
significantly faster (up to 30% best case) data transfer speed
from the silver to the disk cache. From there on to the disk
controller and the buffers, it's all the same.
This was explained to me by a guy that works on firmware
for Seagate. He sent me the best "disk speed measure" program
I've ever seen!
Cheers
Nuno Souto
[EMAIL PROTECTED]
http://www.users.bigpond.net.au/the_Den
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Author: Nuno Souto
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Author: Haskins, Ed
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