On Jan 5, 2009, at 9:44 AM, D Stubbs wrote:
>
> I suppose it is some kind of 'virtual directory'?
> What makes no sense yet to me is how, say partition #3 could go  
> bad, and not the others - if it they all bunched together.

The following is vastly simplified, and there are a lot of  
exceptions, but should explain things.

There are 2 types of disk problems, hardware and software.

Many software problems with a partition are because of directory  
problems within that partition. If the directory of partition A gets  
trashed for whatever reason, the directories of partitions B and C  
are not affected, since they are completely independent "virtual  
disks". Think of this type of problem as if you had 3 firewire  
external disks daisy chained together (or for old school folks,  
multiple SCSI disks). If one disk went bad, the other 2 should still  
work with no problems.

Hardware problems can affect 1 partition, multiple partitions or the  
whole mechanical drive. Examples:

Say that there is a head crash that scratches a small portion of one  
of the platters. If the head is OK, this will most likely affect a  
small portion of one of the partitions, unless it is part of the  
directory. It should not affect the other partitions.

Now imagine that that same head crash destroyed the head. This could  
affect either 1 partition (if it is the large partition which spans  
multiple platters) or multiple partitions if they are on the same  
physical platter (your 2 smaller partitions).

Lastly are things that cause total disk failure. Some examples:

The head crash is epic and spews parts of the platter or heads around  
the inside of the drive.
Power surge that trashes the controller board.
Spindle bearing failure that keeps the disk from spinning.

If something like this happens, all partitions are gone and it is  
time to restore from your backup (cheap) or call DriveSavers with  
your AmEx Black card.

HTH,
Len

  

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