At about 400 GB I picked up 4 errors, then nothing for a long time. I
left the house for a while and came back to this, which seems bad:
$ sudo ddrescue -v -n --force /dev/sda /dev/sdb ddrlog.txt
GNU ddrescue 1.19
About to copy 2000 GBytes from /dev/sda to /dev/sdb.
Starting positions: infile = 0 B, outfile = 0 B
Copy block size: 128 sectors Initial skip size: 128 sectors
Sector size: 512 Bytes
Press Ctrl-C to interrupt
rescued: 951404 MB, errsize: 1048 GB, current rate: 0 B/s
ipos: 2000 GB, errors: 63, average rate: 49658 kB/s
opos: 2000 GB, run time: 5.32 h, successful read: 4.53 m ago
Finished
It's a 2 TB HDD, so it looks like it did half of it.
Any opinions on the best next step?
Mike
On Sun, 13 Sep 2015, Mike Miller wrote:
> Thanks again, Dan. I ended up starting it before getting your message below,
> but I think I've got it right. /dev/sdb1 was working and I backed up all of
> it. /dev/sda1 couldn't be mounted, but they previously were cloned. So I
> unmounted /dev/sdb, installed GNU ddrescue (on a third drive) and did this:
>
> sudo ddrescue -v -n --force /dev/sda /dev/sdb ddrlog.txt
>
> After that finishes, I will run this to try to get the bad parts:
>
> sudo ddrescue -v -r1 /dev/sda /dev/sdb ddrlog.txt
>
> (I'm not sure if I need --force with the second command, but I was forced to
> use it with the first command.)
>
> The first command has been running for 45 minutes so far and it reports zero
> errors and 100 MB/s average throughput. So far, so good.
>
> Mike
>
>
> On Sun, 13 Sep 2015, Dan Armbrust wrote:
>
>> On 09/12/2015 03:21 PM, Mike Miller wrote:
>> Wow, Dan, thanks so much for all the ideas! This is a huge help.
>> Here's what's going on:
>>
>> I already formatted the new drive with ext4 and copied 3 TB of data
>> onto it, so I don't want to undo all that right away, but there is another,
>> probably more appealing way to go:
>>
>> /dev/sda and /dev/sdb are identical 2 TB drives that were previously
>> in a RAID1. It looks like sdb somehow disconnected from the RAID, but sda
>> kept working for a few months before it
>> failed. I can mount /dev/sdb1 just fine and I copied all the files
>> off of it onto the new external drive. I had no errors. So maybe /dev/sdb
>> is in pretty good shape. Now that it's backed
>> up, maybe the best plan is to try to copy /dev/sda to /dev/sdb using
>> one of the dd tools.
>>
>> So here's a question: /dev/sdb is formatted for ext4. If I want to
>> use it as the destination drive for the dd copy, do I have to use parted to
>> remove the partition table first? Or what?
>>
>> Thanks again!
>>
>> Mike
>>
>>
>> You don't have to worry about the partition tables or anything - because
>> rather than copying a partition - such as /dev/sda0 you will just be
>> copying the entire disk - so /dev/sda.
>>
>> When you copy the old (failing) disk onto the other disk (that is either
>> the same size, or larger) you will be copying _everything_ - including the
>> partition table, and the formatting info of the file
>> system. The contents of the disk you are writing to will be completely
>> overwritten.
>>
>> So then your replacement disk will be (exactly) what the failing disk was,
>> partition table, labels, filesystem and all. Though, you will likely have
>> some subtle corruption where blocks that couldn't be
>> read have the wrong bit value.
>>
>> So, if you do manage to recover some things - keep in mind that some of the
>> files my have subtle corruption.
>>
>> Will you notice if 8 bits are flipped in a 2 GB movie? Probably not... but
>> you would really just have to test the more important files that you
>> recover to make sure they aren't worse than your several
>> month old backup.
>>
>> Dan
>>
>>
>