HP XP P9000Watch and HP XP P9000Sketch Reference Guide for HP XP P9000 Performance Advisor v5.5 (T1789-96341, February 2013)

C Relationship between LDEV I/O response time and Write
ratio
We cannot establish a relationship between the LDEV I/O response time and Write ratio because:
• LDEV I/O response time is dependent on both front-end reads and front-end writes.
• Write ratio provides only the write percentage in the I/Os.
NOTE: The LDEV I/O response time shown by HP XP P9000Watch is the average I/O response
time measured in milliseconds (that is, both reads and writes together are responsible for variations
in this value).
The LDEV response time in HP XP P9000Watch is calculated using the formula:
(front-end read response time over the collection interval * front-end reads + front-end writes *
front-end write response time over the collection interval) / (total front-end I/O)
where:
• front-end reads = front-end random reads + front-end sequential reads
• front-end writes = front-end random writes + front-end sequential writes
• Total front-end I/O = front-end reads + front-end writes
70 Relationship between LDEV I/O response time and Write ratio