craigm said:
SgtMinor wrote:
Can you explain what you mean about not being in the path of the r/w heads?
Steve Gibson, the creator of Spinrite, explains that over time the
heads can drift from the position they had when the data was first
written to the sector. As a result the now mis-aligned heads can
no longer access that data and thus the sector may be marked as
"bad." The DynaStat component of SpinRite jolts the heads across
the platter in an attempt to locate those heads back over the
place the data was written. It then reads that data and rewrites
it. Here's how it's explained in the SpinRite documentation:
"During this exhaustive rereading, DynaStat employs its second
recovery strategy of deliberately wiggling the drive's heads. By
successively approaching the troubled sector from different
distances and directions, the heads arrive at the sector's track
at different velocities, which in turn produce small but
significant displacements in the head's resting position. This
allows DynaStat to compensate for the long-term alignment drift
that occurs in non-servo based drives, and the positioner
hysterysis that occurs in servo-based designs.
Thus the drive's heads are given every opportunity to land in the
best possible location to correctly read the sector. This approach
is also extremely effective at recovering data from misaligned
diskettes – which SpinRite 3.1 is proving to be extremely
effective upon."
You can hear the clattering sounds from the hard drive when
SpinRite does its thing. It's a great program and I highly
recommend it to people who are trying to extract valuable data
from "bad" sectors.
See "SpinRite's Technology" on this page:
http://www.grc.com/srdocs.htm