RE: HYPER VOLUMES - RE: "Never split index and data files ..."

From: Haskins, Ed <Ed.Haskins_at_VerizonWireless.com>
Date: Tue, 24 Apr 2001 10:00:19 -0700
Message-ID: <F001.002F0831.20010424081556@fatcity.com>

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
nsouto_at_nsw.bigpond.net.au
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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Received on Tue Apr 24 2001 - 12:00:19 CDT