FlashCopy statistics collection
The system collects FlashCopy® specific metrics, which allows support to analyze performance issue.
Introduction
FlashCopy statistics measures the I/O amplification and magnification in FlashCopy layer, and it also measures the latency of the FlashCopy I/O operations. The various cache statistics gives information regarding the various FlashCopy I/O stages, though it is not obvious where the amplification or magnification is originating. Therefore, FlashCopy will track and measure the internal operations that are required to process an I/O in FlashCopy.
Statistics types
- Aggregate statistics: The aggregate duration in microseconds(XXag) and the maximum duration in microseconds (XXmx).
- Count statistics: A count(XXcn) is just a simple count, this doesn't get reset.
The aggregate statistics(XXag) and count statistics(XXcn) are cumulative. This way if there are two different files (from any time), you can calculate the average response time between the two files. The maximum will be reset after each sample period.
Tables
The following tables describe the information that is reported for individual volumes.
The below table describes the statistics collection for Volume aggregate statistics.
| Statistic name | Description |
|---|---|
| wlag, wlcn, wlmx | Indicates Write Lock Requests, these will be against the client volume. Note: This will
include cleaning I/O.
|
| rlag, rlcn, rlmx | Indicates Read Lock Requests, these will be against the client volume. |
| bcag, bccn, bcmx | Indicates Background Copy Operations, these will be against the target, that is, the volume being copied to. |
| clag, clcn, clmx | Indicates Cleaning Operations, these will be against the target being cleaned, that is, the volume being copied from. |
| rwag, rwcn, rwmx | Indicates ROW copy Operations, these will be against the client volume. |
| twag, twcn, twmx | Indicates Host Write I/O Operations at top of FlashCopy, these will be against the client volume. |
| trag, trcn, trmx | Indicates Host Read Operation at top of FlashCopy, these will be against the client volume. |
| bwag, bwcn, bwmx | Indicates Write Operations at bottom of host I/O, these will be against the client volume of the host IO. |
| brag, brcn, brmx | Indicates Read Operations at bottom of FlashCopy for host I/O, these will be against the client volume of the host IO. |
The below table describes the statistics collection for Volume count statistics.
| Statistic name | Description |
|---|---|
| hwsg | Indicates Host Write Split Grain. The number of grains split due to host I/O for this volume, this will be against the client volume. |
| hwdg | Indicates Host Write Diff Grain. The number of grains marked as different due to host I/O for this volume, this will be against the client volume. |
| srcp | Indicates Successful ROW copy. The number of successful ROW copy operations, this will be against the client volume. |
| twbl | Indicates Host Write Blocks at top of FlashCopy, this will be against the client volume. |
| trbl | Indicates Host Read blocks at top of FlashCopy, this will be against the client volume. |
| bwbl | Indicates Write Blocks at bottom of FlashCopy for Host I/O, this will be against the client volume for the host I/O. |
| brbl | Indicates Read Blocks at bottom of FlashCopy for Host I/O, this will be against the client volume for the host I/O. |
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