Cache hit rates
Function
The cache hit rate is a rate that the input or output data of the disk exists in the cache. The cache hit rate is displayed for the sequential access mode, the random access mode, and the entire these modes.
- Read hit ratio
For a read I/O, when the requested data is already in cache, the operation is classified as a read hit. For example, if ten read requests have been made from hosts to devices in a given time period and the read data was already on the cache memory three times out of ten, the read hit ratio for that time period is 30 percent. A higher read hit ratio implies higher processing speed because fewer data transfers are made between devices and the cache memory.
- Write hit ratio
For a write I/O, when the requested data is already in cache, the operation is classified as a write hit. For example, if ten write requests were made from hosts to devices in a given time period and the write data was already on the cache memory three cases out of ten, the write hit ratio for that time period is 30 percent. A higher write hit ratio implies higher processing speed because fewer data transfers are made between devices and the cache memory.
Storing period
Sample Interval can be specified from 1 to 15 minutes.
Selection of monitoring objects
Select the desired monitoring objects in the Performance Objects field.
|
Item on left side of Object field |
Item on right side of Object field |
Item on left side of Monitor Data field |
Item on right side of Monitor Data field |
|
Logical Device* |
Base |
Cache Hit (%) |
|
|
UR |
Initial Copy |
Cache Hit (%) | |
|
Parity Group* |
None |
Cache Hit (%) |
|
|
LUN* |
Base |
Cache Hit (%) |
|
|
UR |
Initial Copy |
Cache Hit (%) | |
|
Entire Storage System |
UR/URz |
Initial Copy |
Cache Hit (%) |
|
Journal |
UR |
Initial Copy |
Cache Hit (%) |
|
* Volumes that do not accept I/O from the host, such as pool-VOLs, are not monitored. | |||