Multipath Statistics

[Lan <transter@gmail.com>]

Hi all,

Thought it would be a good time to bring up a discussion on the type
of statistics that dm-multipath would find useful, e.g. for a load
balancing path selection algorithm or for users. This is a list of
statistics provided by an IBM multipathing product. (The discussion of
how to gather these type of statistics would also require another
discussion). Any thoughts/suggestions?

Per Path Information:	 
- Number of times the path was selected for I/O
- Number of I/O errors on this path
	
Per Adapter Information	:
- The number of times this adapter was selected for I/O
- The number of errors on all paths attached to this adapter
- The number of paths attached to this adapter
- The number of functional paths attached to this adapter (i.e.
Exclude failed or offline paths)
   
Path Performance Information (more specific breakdown):  	
Total Read I/O:	Total number of completed read requests
Total Read Sector:	Total number of sectors that have been read
Total Write I/O:	Total number of completed write requests
Total Write Sector:	Total number of sectors that have been written
Active Read I/O:	Total number of read requests in process
Active Read Sector:	Total number of sectors to read in process
Active Write I/O:	Total number of write requests in process
Active Write Sector:	Total number of sectors to write in process
Maximum I/O:	The maximum number of active I/O requests
Maximum Sector:	The maximum number of active sectors to read or write
Transfer Size:	
<= X , (X = {512, 4K, 16K, 64K})	The number of I/O requests received
whose transfer size is X bytes or less
> 64K 	The number of I/O requests received whose transfer size is greater than 64KB
	
Adapter Performance Information:
** identical to Path performance information except no "Transfer Size'" info


Thanks!
Lan