Async Pin Reads/sec is the frequency of reading data into the file system cache preparatory to writing the data back to disk. ...

Async Pin Reads/sec is the frequency of reading data into the file system cache preparatory to writing the data back to disk.  Pages read in this fashion are pinned in memory at the completion of the read.  The file system will regain control immediately even if the disk must be accessed to retrieve the page.  While pinned, a page's physical address will not be altered.