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For each device
in the terminal, the terminal agent keeps count of i/o operations
to the device and counts adverse events that are reported for the
device. The counts are kept in what we call “InSight Operational
Statistics Table” format. The design intent of tracking this
information and how we track it is to enable positive or negative
trends to be noticed and to support “check engine” type
functionality using very little memory or disk space.
The operational
statistics table consists of rows that can be grouped into two
groups. The first group consists of 6 rows containing operational
statistics for the past hour. Rows in the first section are updated
every minute. The second group (rows 7 and above) are “history
rows”. History rows are created by periodically making snapshot
copies of one of the rows from the first group.
A row in this
table includes the following fields: ending date/time of interval,
i/o event count, adverse event count.
Row 1 contains
counts since the last minute change. Row 2 is for the previous
minute. Rows 3 - 6 are previous 5, 15, 30, and 60 minutes
respectively.
One of rows 2-6
can be chosen as the base for the history rows. The default is the
60-minute row. History rows snapshots are taken “on the mark” - so
the 60 minute row is copied on the hour to history row 7 after
rolling down the existing history rows. A fixed maximum number of
history rows are kept. The default is 24 history rows.
The adverse event
info table keeps track details on the last 10 adverse events. When
an adverse event is detected, details are copied to the adverse
event info table.
Finally, a word
about i/o events and adverse events. In order to make the
information as useful as possible, there have been judgments made
about which i/o operations to count and which adverse events are
“normal” and which are truly adverse. For example, for the 4610
printer, only write events are counted. Reads are actually totally
handled in the printer driver -> no work is done in the printer
as a result of the read. Similarly, “document not present” errors
are not counted as adverse events because these are encountered as
part of normal processing.
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