2009-09-07 16:03:00 UTC
The P List is an odd one. If I bought a 320Gb hard drive, that's
exactly what I'd expect to see on it. So it sounds like hard drives
have extra capacity to account for manufacture problems. The P List
will point to the physical sector on a hard drive that replaces the
logical sector whose physical counter-part is b0rked.
OK, that's all well and fine - just about. But it gets odder when you
now consider the G List.
The G list is like the P list, but this grows during the lifetime of
the drive. Again, I suspect extra capacity comes into play, but once
the list is full, you best be replacing your drive. Note: apparently,
only until that list is full, do you realise your sectors have been
pegging out as the hard drive can no longer shield you from the truth.
Now, surely this makes a mockery of defragging your drive.
If a sector goes bad and is transparently replaced by another from the
spare pool, one hopes that the new physical sector is nearby where it
should have been, otherwise defragging will not be effective. You
could end up with also sorts of oddly mapped files on your hard-drive,
but your OS would report them as contiguous.
This also affects EXTn file systems so beloved of us open-sores types.
These systems pride themselves in minimal fragmentation because they
always seek to put down a file in as big a set of contiguous sectors
as possible. Well, that's fucked right out of the water by all of this
P and G List business.
So, why do we bother defragging, or using EXTn if our hard drives do
this list business?