Comment 14 for bug 607560

After much investigation, i discovered that the output of "hdparm -B /dev/sda" happen to be my only laptop hard drisk, gives me a value of 128, which permits the HD from spinning down. This is what is prevents the hard driver from spinning down and not the jbd2 activity. BTW, I did a complete fresh install.

from hdparm man page (notice the bit about 128 being in the range that prevents spinning down):

   -B Query/set Advanced Power Management feature, if the drive sup‐
              ports it. A low value means aggressive power management and a
              high value means better performance. Possible settings range
              from values 1 through 127 (which permit spin-down), and values
              128 through 254 (which do not permit spin-down). The highest
              degree of power management is attained with a setting of 1, and
              the highest I/O performance with a setting of 254. A value of
              255 tells hdparm to disable Advanced Power Management altogether
              on the drive (not all drives support disabling it, but most do).