Re: [Bug-ddrescue] Doesn't seek when reading from tape.

[Ariel]

On Thu, 5 Oct 2006, Grzegorz Nowakowski wrote:

> 5. after tape is repositioned at 0 and ddrescue is restarted with log
>  file, it will append new data at the end of output file, but it will
>  read it from the beginning of the tape;

ddrescue depends on the operating system to position the data it reads.

I don't know a lot about tape drives, but from what I understand if you 
use the character device to read from the tape it reads sequentially from 
the tape, and does not do any sort of positioning.

However, at least for the docs of the driver I read, sometimes you are 
also provided with a block device for the tape drive.

The point of the block device is that it automatically positions the tape 
based on where you seek to in the block device.

See if you can find a block device for your tape drive.

You can tell if it's a block or character device by running ls -l on the 
device file.

If the first letter of the output is c it's a character device, b is a 
block device.

A character device will not work with ddrescue, since character devices 
only read sequentially, and have no ability to seek.

BTW: this is the same problem that is causing the drive to stop after an 
error. ddrescue sees the error and (tries to) seek to a later spot, but a 
character device has no seek, so the tape doesn't move. ddrescue reads 
data, and again gets the error data, since the tape is in the same place 
it was before.

        -Ariel