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Re: [Bug-ddrescue] Best options for rescuing a DVD?

From: Harri Järvi
Subject: Re: [Bug-ddrescue] Best options for rescuing a DVD?
Date: Sun, 19 Jun 2011 23:58:35 +0300
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv: Gecko/20110506 Icedove/3.0.11

On 19.06.2011 09:38, Ian Oliver wrote:
The third is different. I'm now in day 3 and have rescued 2471MB. I
don't know how much data is on the disk: ddrescue went for all 4GB+ but
I suspect that some sectors are missing at the start such that the size
is unknown. Which driver/layer/device is responsible for determining
size of tha DVD?

It is the responsibility of the block device subsystem of the kernel to determine the size of the block device.

You can query the block device size in bytes from the kernel by running the command

blockdev --getsize64 /dev/cdrom

Notice that the SCSI specification allows to report 75 of 2k-blocks more than the actual size. Thus, the block device subsystem may also report a bit too high a number. (drivers/scsi/sr.c)


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