HP XP Performance Advisor Software - Manual (Page 59)

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 XPWatch 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 XPWatch 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
XPWatch and XPSketch Reference Guide 59