Our data recovery process almost always begins with a copy process. Otherwise known as cloning or imaging, we attempt to copy every data block from the failed disk to another disk.
With a normal disk, we can record how long it takes to copy a block, then multiply by the total number of blocks to calculate how long the process will take.
With a faulty disk, this is not possible. A faulty disk will often read different blocks at different speeds depending on how bad the problem is. Until we read the block, there’s no way to know how long it will take. This is illustrated in the animation below. (Sorry, the GIF below is quite large so may take a while to load.)
With a faulty disk, we have to keep copying blocks until we get all the data. You can see from the animation above that it’s impossible to know how many slow blocks are coming up, versus good blocks.
This is the third part of a mini-series about copying data.
Read Part One here about copying small vs large files.
Read Part Two here about why computers always guess the wrong copy time.
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