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Bandwidth Limitations of Platter Disk

The limitations of the magnetic-coated disk platters have been well understood since they were first invented nearly a half century ago.  Back in the day of Data Processing, disks were much smaller, and Oracle databases could get additional bandwidth by having the data files reside on multiple disk spindles with more disk controllers (Figure 2.3):

The Problem of Super-large Disks

Over the decades, disk manufacturers continued to make disk devices larger, ignoring the bandwidth limitations imposed by locating all of the data storage on a single device.  As of 2005, it is very difficult to purchase a disk spindle that is less than 100 gigabytes, and this causes disk I/O bandwidth issues at two levels (Figure 2.4):

  • Bandwidth limitations within the disk as a result of excessive read-write head movement

  • Controller bandwidth limitations

Today’s super-large disks allow the Oracle DBA to place an entire database onto a single pair of mirrored devices.  This imposes a severe data transmission bottleneck, especially when concurrent requests for data are made for data on different cylinders.  This can cause the disk to shake like an unbalanced washing machine in the spin cycle, and seriously impede the ability of Oracle to deliver information to an application.

The next section will explore some methods for removing this technology imposed bandwidth limitation and see how SSD can increase throughput for almost all Oracle databases.


The above book excerpt is from:

Oracle RAC & Tuning with Solid State Disk

Expert Secrets for High Performance Clustered Grid Computing

ISBN 0-9761573-5-7

Donald K. Burleson & Mike Ault

http://www.rampant-books.com/book_2005_2_rac_ssd_tuning.htm

  
 

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