Chapter 8: Statistics
Statistic | Description |
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Write Cluster Rate | This is the percentage of the number of write commands |
| that are part of a cluster versus the total number of write |
| commands that have been issued. This gives an |
| indication of the sequential nature of the data access |
| pattern from the host and of the performance of the |
| writeback cache. |
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RAID 5/50 Partial Command | This is the percentage of the number of clustered |
Cluster Rate | commands that wrap around the end of a stripe versus |
| the total number of clustered commands. This gives an |
| indication of the alignment of the operating system. |
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RAID 5/50 Full Stripe Write | This is the percentage of the amount of data that is |
Rate | written as a full stripe write versus the total amount of |
| data written. This gives an indication of the sequential |
| nature of the data access pattern from the host and of |
| the performance of the writeback cache, for RAID 5/50 |
| drive ranks. |
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Command Cluster Interval | In determining whether to cluster write commands, the |
| controller will search back in the command queue |
| whenever it receives a new write command. In a multi |
| threaded operating system, commands from each |
| thread can be interspersed with commands from |
| another thread. This requires that the controller not just |
| check the immediately previous command. The |
| controller will search back for a number of commands, |
| to try to determine if the new command is exactly |
| sequential to any one of these previous commands. If |
| it is, then the controller determines that it can cluster |
| these commands. |
| These statistics record the average and maximum |
| number of commands the controller must search back |
| for when it finds a sequential command match and the |
| percentage for each one of these values. |
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Command Cluster Count | When the controller clusters a write command, it can |
| cluster a large number of them together. These |
| statistics record the average and maximum number of |
| commands the controller clusters and the percentage |
| for each one of these values. |
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