HP P2000 G3 MSA - Document Conventions and Symbols

Technical white paper | HP P2000 G3 MSA
6
Shared LUN number between controllers with a maximum of 512 LUNs
• No duplicate LUNs allowed between controllers
• Either controller can use any unused logical unit number
ULP recognizes which paths are “preferred”
• The preferred path indicates which is the owning controller per ALUA specifications
• “Report Target Port Groups” identifies preferred path
• Performance is slightly better on preferred path
Write I/O Processing with ULP
• Write command to controller A for LUN 1 owned by Controller B
• The data is written to Controller A cache and broadcast to Controller A mirror
• Controller A acknowledges I/O completion back to host
• Data written back to LUN 1 by Controller B from Controller A mirror
Figure 1. Write I/O Processing with ULP
Read I/O Processing with ULP
• Read command to controller A for LUN 1 owned by Controller B:
– Controller A asks Controller B if data is in Controller B cache
– If found, Controller B tells Controller A where in Controller B read mirror cache it resides
– Controller A sends data to host from Controller B read mirror, I/O complete
– If not found, request is sent from Controller B to disk to retrieve data
– Disk data is placed in Controller B cache and broadcast to Controller B mirror
– Read data sent to host by Controller A from Controller B mirror, I/O complete