Split IO meaning

[Max Pierre]

Hi,

What does a split IO really mean ?
For example :

Performance monitor gives 1 split IO/sec for 1 Disk Transfers/sec.

Does it mean that one IO requested from the driver is served by

a) two physical IOs ?
b) one IO and several IOs grouped as one split IO

From a graph, we see 120 disk transfers/sec and 50 Split IO/sec. Does it mean that the disk served 70 "non splitted" IOs and 50 IOs resulting from IOs that were splitted ?

Explanation from TechNet does not help.

"Reports the rate at which the operating system divides I/O requests to the disk into multiple requests. A split I/O request might occur if the program requests data in a size that is too large to fit into a single request or if the disk is fragmented. Factors that influence the size of an I/O request can include application design, the file system, or drivers. A high rate of split I/O might not, in itself, represent a problem. However, on single-disk systems, a high rate for this counter tends to indicate disk fragmentation."

Thanks in advance for your help

[Ali]

Hi Max,

what I understand from Split IO parameter is that If the disk is more than 20% fragmented, Split I/O counter splits a single request into multiple requests.

fragmentation reduces performance by causing excessive seek time.


You may use the Windows Disk Defragmentation tool to defragment the disk.

this link has little better explanation.
http://blogs.technet.com/b/cotw/archive/2009/03/18/analyzing-storage-performance.aspx

thanks,
Aftab