Gateway 840 VT-100, User Manual

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Viewing readahead statistics
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Viewing readahead statistics
If sequential read commands are sent to the controller, it assumes that the commands
that follow can also be sequential. It can then go and perform a read of the data
before the host requests it. This improves performance, particularly for smaller reads.
The size of the readahead is calculated based on the original command size, so the
controller does not read too much data. The controller maintains statistics for all
readahead commands performed.
The View Readahead Statistics screen is accessed by going to the Statistics Types menu
(see “Viewing all statistics” on page 155 ), then selecting
View Readahead Statistics
.
Statistic Description
Readahead Command Hit
Rate This is the percentage of read command hits versus the
total number of read commands that have been issued.
This gives an indication of the sequential nature of the
data access pattern from the host.
Readahead Command
Efficiency This is the percentage of the number of read command
hits versus the projected number of readahead
command hits. This is a measure of the efficiency of the
readahead algorithm. A low value means that much of
the data that the controller reads in the readahead
command is not actually requested by the host.