What are Mode Pages, and How are they Used?

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Mode page commands are used to read or set a wide range of device parameters. They are applicable to all devices that use the SCSI command set. This includes SCSI tapes, fibre channel disk drives, and SCSI CDROMs and disk drives. IDE disk drives do not use mode pages, nor do CDROMs that use the IDE interface.

 

Mode pages should never be changed unless you completely understands its function. As they make fundamental changes to the way a device operates, improper settings can destroy data or render a device invisible to the operating system. Conversely, proper settings of mode pages can have significant performance benefits. For example, generally IBM disables write cache on your disk drives. If you are in a write-intensive environment, you might almost double performance by enabling it. (At the risk of data loss if you do not have a UPS connected to your computer and you have a power failure).

 

Your computer and disk drive vendors are the best source for determining how to best modify mode pages for your operating system and what types of programs you run.  They may also tell you if certain mode pages are not supported by them, as they might sacrifice data integrity for performance.

 

This document does not provide a tutorial on what each mode page does, and how it is used. We just supply you software which allows you to view and manipulate mode pages.

 

The ANSI specification defines a set of mode pages which are typically found in many devices. As most people are concerned with mode pages specific to disk drives, some of them are shown below to give you an idea of what they are good for.  Manufacturers are also free to define vendor-specific pages. Some may be documented online in their disk drive programming specification manuals. Other pages may only be available under a non-disclosure agreement.