Viewing readahead statistics
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 |
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|
Readahead Command Hit | This is the percentage of read command hits versus the |
Rate | 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 | This is the percentage of the number of read command |
Efficiency | 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. |
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