Note:  R/W stands for Read and Write operations. 

GLYPH<SM590000> I/O Rate R/W : The term I/O  is used to describe any program, operation, or device that transfers data to or from a computer, and to or from a peripheral device. Every transfer is an output from one device and an input into another. Typically measured in IOPS. 

GLYPH<SM590000> Data Rate R/W : The data transfer rate (DTR) is the amount of digital data that is moved from one place to another in a specific time. In case of Disk or Storage Subsystem, this metric is the amount of data moved from a host to a specific storage device. Typically measured in MBps. 

GLYPH<SM590000> Response time R/W : This is the time taken for a circuit or measuring device, when subjected to a change in input signal, to change its state by a specified fraction of its total response to that change. In case of Disk or Storage Subsystem, this is the time used to complete an I/O operation. Typically measured in ms. 

GLYPH<SM590000> Cache Hit R/W : This is the percentage of times where read data or write data can be found in cache or can find cache free space that it can be written to. 

GLYPH<SM590000> Average Data Block Size R/W : The block size is the unit of work for the file system. Every read and write is done in full multiples of the block size. The block size is also the smallest size on disk that a file can have. 

GLYPH<SM590000> Port-to-Local Node Queue Time (Send) : The average time in milliseconds that a send operation spends in the queue before the operation is processed. This value represents the queue time for send operations that are issued to other nodes that are in the local cluster. A good scenario has less than 1 ms on average. 

GLYPH<SM590000> Port Protocol Errors (Zero Buffer Credit Percentage) : The amount of time, as a percentage, that the port was not able to send frames between ports because of insufficient buffer-to-buffer credit. The amount of time value is measured from the last time that the node was reset. In Fibre Channel technology, buffer-to-buffer credit is used to control the flow of frames between ports. In our experience less is better than more. However, in a production environment this metric can be from 5% on average up to 20% peak without affecting performance. 

GLYPH<SM590000> Port data rate (send and receive) : The average number of data in MBps for operations in which the port receives or sends data. 

GLYPH<SM590000> Port Protocol Errors (Zero Buffer Credit Timer) : The number of microseconds that the port is not able to send frames between ports because there is insufficient buffer-to-buffer credit. In Fibre Channel technology, buffer-to-buffer credit is used to control the flow of frames between ports. Buffer-to-buffer credit is measured from the last time that the node was reset. This value is related to the data collection sample interval. 

GLYPH<SM590000> Port Congestion Index:  The estimated degree to which frame transmission was delayed due to a lack of buffer credits. This value is generally 0 - 100. The value 0 means there was no congestion. The value can exceed 100 if the buffer credit exhaustion persisted for an extended amount of time. When you troubleshoot a SAN, use this metric to help identify port conditions that might slow the performance of the resources to which those ports are connected. 

GLYPH<SM590000> Global Mirror (Overlapping Write Percentage) : The percentage of overlapping write operations that are issued by the Global Mirror primary site. Some overlapping writes are processed in parallel, and so they are excluded from this value. 

GLYPH<SM590000> Global Mirror (Write I/O Rate) : The average number of write operations per second that are issued to the Global Mirror secondary site. Keep in mind that IBM SAN Volume Controller / Storwize systems have limited number of GM I/Os that can be delivered. 

