On 2011/10/04 09:34, John Martz so eloquently wrote:
My understanding is it works this way. If the drive attempts to read a
sector and the read fails, the sector is marked as "pending". It is
not remapped under the rational that the read may succeed in the
future. So if you see a non-zero value for pending sectors in the
drive's SMART data, this is what has happened.
If you write to a sector and the write fails THEN the sector is
remapped (if possible). This is tallied in the Reallocated Sectors
Count, I think. The drives firmware keeps track of the remapping and
reads/writes to that sector redirected from that point on to the
remapped sector.
The gist is that if you have bad sectors and you want to force the
drive to remap them you have to write to those sectors. One way to do
this is to perform an erase of the drive i.e. write zeros (or
whatever) to every sector on the drive.
A format in and of itself may do nothing. It all depends on what
sectors on the drive the format writes to. FWIW, I'm not sure what the
phrase "low level format" means with any drive sold this century. For
quite some time the format of a hard drive is fixed once it leaves the
factory and this can't be tinkered with other than remapping bad
sectors via the firmware.
And, yes, if you have a large number of either pending or reallocated
sectors on a drive, it is a cause for concern about the health of the
drive. Especially if the number keeps going up.
FWIW, I looked this up on Micromat's website and it said that their
write zeros function does not map out bad sectors. They suggested using
Disk Utility.app, though there may be other 3rd party apps that can do
it too.
My main concern is if I do a low level reformat with all zeros, and then
at a later date reinitialize the drive, would it then lose it's updated
map and revert to the factory's map?
Tina
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