Re: [gentoo-user] data recovery advice needed

[Mick <michaelkintzios@gmail.com>]

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On Tuesday, 18 December 2018 18:51:55 GMT Grant Taylor wrote:
> On 12/18/2018 10:42 AM, Mick wrote:
> > I know others have commented on the reliability of recovering data from
> > drives connected via USB caddy, but I have had satisfactory results on a
> > number of cases.
> 
> I think it completely depends on the type of problem.  In my experience,
> SATA-to-USB adapters don't deal well with physical hard drive / media
> errors.  (At least compared to SATA connections on the motherboard.)  I
> think their retry mechanisms are somewhat limited.  Conversely, software
> / file system / logical corruption issues are likely perfectly fine over
> USB.

I ran ddrescue while the drive was still on the laptop.  The clone was on the 
USB caddy.


> > I cloned the whole drive having run ddrescue backwards and forwards a
> > couple of times.  c/f/gdisk would see all partitions, but when I tried to
> > mount the cloned /dev/sdb4 (NTFS) with ntfs-3g it complained there was no
> > device found (/dev/sdb4).  I got the same error with the failing drive.
> 
> Seeing the partitions in the partition table is independent of the
> device file being there.  -  Did the device file exist?  -  I
> occasionally have to run (k)part(x) to tell the kernel that the
> partition is there and to create the device file.

The disk block device is there and so is the first partition (only):

ls -la /dev/sdb*
brw-rw---- 1 root disk 8, 16 Dec 19 11:20 /dev/sdb
brw-rw---- 1 root disk 8, 17 Dec 19 11:20 /dev/sdb1


However, there's 6 partitions in total:

Disk /dev/sdb: 1953525168 sectors, 931.5 GiB
Model: LucidPort USB300
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 1A95F5D1-5630-4E06-9DC3-36841C786DDF
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1953525134
Partitions will be aligned on 2048-sector boundaries
Total free space is 4770 sectors (2.3 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          821247   400.0 MiB   2700  Basic data partition
   2          821248         1353727   260.0 MiB   EF00  EFI system partition
   3         1353728         1615871   128.0 MiB   0C01  Microsoft reserved 
...
   4         1615872      1911737034   910.8 GiB   0700  Basic data partition
   5      1911738368      1915412479   1.8 GiB     2700  
   6      1915412480      1953523711   18.2 GiB    0700  Basic data partition

I can see partition 4 I was trying to recover, but could not add it:

partx --show --nr 4 /dev/sdb
NR   START        END    SECTORS   SIZE NAME                 UUID
 4 1615872 1911737034 1910121163 910.8G Basic data partition fea85fb3-
cfdb-4868-a1ad-bab264dad237

partx --add --nr 4 /dev/sdb
partx: /dev/sdb: error adding partition 4

partx --add /dev/sdb
partx: /dev/sdb: error adding partitions 1-6

In any case, losetup with offset/size succeeded in mounting it and I was able 
to access the fs on it.
-- 
Regards,
Mick

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