User manual

Frequenty Asked Questions 229
SANTOOLS® is registered in US Patent and Trademark Office No 3,107,854 All rights reserved.
Interval Exceptions
(But if 6 not
supported, it
tries 4, then 3)
sent in response to a request for it.
MRIE of 4 means that the disk will unconditionally generate a
CHECK CONDITION (recovered error) sense error on I/Os
when/if disk becomes degraded and SMART kicks in.
Setting bit to 3 conditionally generates the same errors,
depending on a mode page setting.
MRIE values of 3 & 4 have higher overhead due to
requirement that log pages are updated once SMART alert
kicks in, but 6 is not supported on all disk drives.
Interval
Timer
Period between
subsequent SMART
error messages
Defaults to 10
minutes
unless -F
command
used to poll more
frequently
The original ANSI spec draft that describes SMART
suggested a 10 minute polling interval. The delay with PERF
off is typically under 400 ms and under 150 ms with PERF on.
You will have to consult your disk drive vendor's
documentation for specific timing values.
Report
Count
# of times to report
SMART status per
interval
0
This means there will be no limit to number of times SMART
is reported in response to a query.
4.3 What are Mode Pages, and How are they Used?
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.
4.4 SES Specific Definitions
For SES, the following definitions, abbreviations, acronyms, symbols, keywords, and editorial conventions apply.
application client: An object that is the source of SCSI commands and destination for responses to commands.
SMARTMon is the application client.
array device: A device in the enclosure, typically a disk drive.
command descriptor block: The structure up to 16 bytes in length used to communicate commands from