There may be a flaw in the method that you used to determine the device
where the dataset's sectors are located.  I think that the store only
reports the device where the file label is located and *not* where the
individual file extents.  It used to be, many moons ago if I remember
correctly, that a dataset would be allocated as a single extent and since
the file label was the first sector of the first extent one would be right
in stating that a dataset resided in a specific device.
 
Use MPEX's listf,4 to see which device your datasets are really on. See
below.
 
My $0.02
 
Regards
 
Paul H. Christidis
 
 
 
-----FILE------ EXTENTS           -----SECTORS-----  DEVICE            LABEL
NAME      CODE  NUM MAX           USED NOW  SAVABLE  CLASS             LDEV
 
PC19      PRIV   18  32            8168992           DISC              29
   Dev/Sector:    3/%0000030225740   2/%0000030406220  22/%0000027236360
   Dev/Sector:   33/%0000030154360  23/%0000027724700  25/%0000030153140
   Dev/Sector:   26/%0000030157060  29/%0000030061460  24/%0000027213460
   Dev/Sector:   27/%0000027233560  35/%0000030574660  31/%0000027246020
   Dev/Sector:   30/%0000027411540  28/%0000031572720  34/%0000030572520
   Dev/Sector:   32/%0000030550720  36/%0000030625060  37/%0000031141640