[Bug-ddrescue] Understanding ddrescue's options and operation

[James W. Watts]

Hello,

I'm trying to better understand the options for ddrescue. I've read the 
ddrescue.info file, but
I'm still confused by some of them.

1. When to stop the ddrescue process?
I currently have ddrescue running as follows: ddrescue --max-retries=3 
--verbose --truncate
--no-split /damaged_drive /good_drive/image_file.img logfile
Are these good options to use? It's been running for about a day. The damaged 
drive is 40GB and
16GB have been rescued so far. The 'current rate' is very slow now, rarely 
climbing above 1kB/s.
I'm not sure how full the drive was, but I'd like to get started on repairing 
the rescued image.

2. --truncate
The .info file says this will "truncate the output file". Let's say I have a 
10GB damaged hard
drive and only 5GB are used. What effect will --truncate have on the resulting 
output image file?
Will it be 10GB, 5GB, or something else? What is being truncated? Is this a 
good option to invoke
to get an image of the non-damaged data?

3. --max-retries=N
ddrescue.info indicates this will cause ddrescue to "exit after given number of 
retries". What is
being "retried"? Reading a bad sector or the entire ddrescue process? Does 
ddrescue exit on its
own if this option is not set or do you have to use Ctrl-C to stop?

4. --no-split
.info says this makes ddrescue "not try to split error areas. Allows a fast 
recovery of the
non-damaged part of the file." Is this related to the --truncate option?

5. --max-errors=N
"Maximum number of errors allowed before giving up. Defaults to infinity."  
What happens if you do
not set this option? What changes if you do? What is causing the "error"? What 
happens when N is
reached (i.e. when it gives up)?

6. --quiet
What effect does this have?

7. How do you know if a hard drive has I/O errors?

8. Which command options should I use if I want ddrescue to make a quick pass 
over the damaged
hard
drive and grab all the good, easy-to-read data? Let's say the damaged drive is 
/dev/hdc and the
good drive to receive the image is /dev/hdd.

9. Finally, help me level-set my expectations. What are some of your typical 
start-to-finish times
for creating a hard drive image? Please specify your HD size and how long it 
took ddrescue to
create the image.

Thanks!

James