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Re: [Bug-ddrescue] user-interface suggestions

From: Richard Neill
Subject: Re: [Bug-ddrescue] user-interface suggestions
Date: Sun, 24 May 2009 19:40:36 +0100
User-agent: Thunderbird (X11/20090330)

Antonio Diaz Diaz wrote:
Richard Neill wrote:
Here lies the problem. It's going to be hard (I think) to write a suitable heuristic for ddrescue.

The problem is that, AFAIK, there is no way for ddrescue to know the block size of a device except by means of user-supplied arguments.

So, how does the user know this? If I sit down at a Linux machine, which has some item of dodgy hardware (probably a regular SATA disk, but maybe PATA, maybe a floppy, maybe a RAID array, or maybe even a USB-disk or a CD-ROM), how am I supposed to find out the block size?

Is this a property of the underlying hardware, of the linux device driver, or of the filesystem?

Googling for this has multiple answers, stating authoritatively that the BS is one of 512, 1k, 2k, 4k or 16k. The only thing I've learned is that "block size" can mean more than one thing.

Is there any way to simplify the heuristic such that ddrescue can make its own decisions about what is "nearly" the best outcome? It doesn't have to be spot on. But at the least, ddrescue should protect the user from any bad consequences of the misuse of -d.

There aren't such bad consequences. If the values supplied are correct, ddrescue will rescue data. If not, all reads will fail fast, but you can stop it and try other values.

Is that obvious to the user? Is it clear from the error message that the error is due to the wrong blocksize specification, and not just because the disk itself is failing? (After all, the user probably *expects* reads to fail because the hardware is broken).

Best wishes,


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