At 11:48 PM -0500 12/11/2011, Barry Levine wrote:
I'm curious about something I noted re my failing 8.6GB SCSI HD.
The drive has 3 partitions - 6GB, 2GB and 600MB. When I run Norton Disk
Doctor, only the 6GB partition has file problems and bad blocks; the other 2
partitions check out ok.
I don't understand this at all; unless perhaps the 2 good partitions are on
a different platter.
Partitions are contiguous blocks of disk space, allocated track by
track, cylinder by cylinder. This is done to make it more efficient
to read large files. eg: move the head once (seek), wait for the
platter to spin around until the target sector(s) arrive under the
head (latency), then read a whole bunch of sectors at once.
Sectors (disk blocks) are "virtual" (software) allocations of space
on a given track. One of the more common ways they go bad is for a
tiny particle of rust (an oxide) that has formed in a pit (no surface
is completely smooth) to become lose. The read or write head then
"wipes" the particle from one sector to the next, to the next, to the
next - along the same track - leaving a gauge in its path. Thus,
sectors tend to go bad in clumps. Eventually centrifugal force
throws the particle off the platter, to the wall the HDA where it
(hopefully) sticks. Of course, there are all sorts of other carnage
scenarios. Shrapnel flying around, etc...
HTH,
- Dan.
--
- Psychoceramic Emeritus; South Jersey, USA, Earth.
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