Does ddrescue Retry For Data Verification?

Topics about disk partitioning (fdisk, parted, gparted, partimage), Volumes Management (lvm, evms, dmraid), Storage, file systems, ...
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Joined: 13 Feb 2016, 17:30

Does ddrescue Retry For Data Verification?

Post by justingoldberg » 13 Feb 2016, 18:21

I am using GNU ddrescue to recover data from a hard drive with bad sectors to a good drive. It is the same sized drive. I pointlessly used badblocks at first, but it did tell me that I have 204 MB in bad sectors. I should have told it to stop at first error.

The source drive that I am cloning/recovering has windows 10 on it. Some of the bad sectors are in the 2 gigabyte "system reserved" partition. I started the recovery on the whole device (/dev/sda) but I want to skip copying the first system reserved partition (sda1) since I expect to be able to copy this partition from another system with the same build and cpu type. I've done this before on a Server 2008 system.

Question 1: can I clone only sda2 (the "real" 465GB windows OS and data partition) and restart the recovery using the same logfile? Skipping the "SYSTEM RESERVED" partition? Eg ddrescue /dev/sda2 /dev/sdb2 /mnt/usb/ddrescue-log.log

Question 2: How do I know the data is good from sectors that have had read errors on the first pass? If the drive gives ddrescue data, how does it know the data is correct without reading the data twice? Or have I been fooled by Spinrite's documentation (it says it rereads sectors 20 times).

Question 3: Can I run ddrescue again to verify the data is good? Does the log show which blocks are good?

My recovery is currently on the second pass. My parameters are ddrescue -d -f -r3 /dev/sda /dev/sdb /mnt/usb/ddrescue-log.log

Posts: 1131
Joined: 07 Apr 2010, 16:19

Re: Does ddrescue Retry For Data Verification?

Post by gernot » 18 Feb 2016, 05:29

You see in the logfile which blocks read with success, are bad or not tried yet.

Blocks read are save because the HD use internal checksums.

You can start to scan with a offset the read the data partition first. Make sure to recover the partition table by time. There are samples in the manual.


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