Re: [gentoo-user] Trouble with backup harddisks

[tuxic@posteo.de]

On 04/30 10:55, Wols Lists wrote:
> On 30/04/20 10:32, tuxic@posteo.de wrote:
> > Hi,
> > 
> > recently I switched from the old MBR-scheme to GPT on
> > my new PC.
> > 
> > I have two external USB-harddisk, which were partioned/formatted with
> > a MBR-scheme/MSDOS partition (but were never used to boot from. They are pure
> > data containers).
> > 
> > When I connect these to my new PC, only the device is shown:
> > /dev/sdb, /dev/sdc.
> > 
> > The kernel is configured (beside other things) as follows:
> > 
> > #
> > # Partition Types
> > #
> > CONFIG_PARTITION_ADVANCED=y
> > # CONFIG_ACORN_PARTITION is not set
> > # CONFIG_AIX_PARTITION is not set
> > # CONFIG_OSF_PARTITION is not set
> > # CONFIG_AMIGA_PARTITION is not set
> > # CONFIG_ATARI_PARTITION is not set
> > # CONFIG_MAC_PARTITION is not set
> > CONFIG_MSDOS_PARTITION=y
> > # CONFIG_BSD_DISKLABEL is not set
> > # CONFIG_MINIX_SUBPARTITION is not set
> > # CONFIG_SOLARIS_X86_PARTITION is not set
> > # CONFIG_UNIXWARE_DISKLABEL is not set
> > # CONFIG_LDM_PARTITION is not set
> > # CONFIG_SGI_PARTITION is not set
> > # CONFIG_ULTRIX_PARTITION is not set
> > # CONFIG_SUN_PARTITION is not set
> > # CONFIG_KARMA_PARTITION is not set
> > CONFIG_EFI_PARTITION=y
> > # CONFIG_SYSV68_PARTITION is not set
> > # CONFIG_CMDLINE_PARTITION is not set
> > # end of Partition Types
> > 
> > CONFIG_BLOCK_COMPAT=y
> > CONFIG_BLK_MQ_PCI=y
> > CONFIG_BLK_MQ_VIRTIO=y
> > CONFIG_BLK_PM=y
> > 
> > dmesg shows this:
> > [14617.672363] usb 2-2: New USB device found, idVendor=1058, idProduct=25a2, bcdDevice=10.21
> > [14617.672364] usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
> > [14617.672364] usb 2-2: Product: Elements 25A2
> > [14617.672365] usb 2-2: Manufacturer: Western Digital
> > [14617.672366] usb 2-2: SerialNumber: 575844314132383959393934
> > [14617.681660] usb-storage 2-2:1.0: USB Mass Storage device detected
> > [14617.681737] scsi host10: usb-storage 2-2:1.0
> > [14618.725450] scsi 10:0:0:0: Direct-Access     WD       Elements 25A2    1021 PQ: 0 ANSI: 6
> > [14618.725594] sd 10:0:0:0: Attached scsi generic sg1 type 0
> > [14618.728090] sd 10:0:0:0: [sdb] Spinning up disk...
> > [14619.748918] ...ready
> > 
> > I tried different USB ports in a desperate hope of success...
> > ...no, same problem.
> > 
> > Interestingly fdisk shows the following:
> > 
> > host> sudo fdisk -l /dev/sdb
> > Disk /dev/sdb: 931.49 GiB, 1000170586112 bytes, 1953458176 sectors
> > Disk model: Elements 25A2   
> > Units: sectors of 1 * 512 = 512 bytes
> > Sector size (logical/physical): 512 bytes / 512 bytes
> > I/O size (minimum/optimal): 512 bytes / 512 bytes
> 
> This could be the key. Sector sizes have been changing from 512 to 4096
> over many years. If your kernel has been updated to expect/use 4096 byte
> sectors, it might not be able to read the disk properly.
> 
> > Disklabel type: dos
> > Disk identifier: 0x16f2a91f
> > 
> > Device     Boot Start        End    Sectors   Size Id Type
> > /dev/sdb1           1 1953458175 1953458175 931.5G ee GPT
> > 
> > The type is shown as GPT...but the drive has a MSDOS partition table.
> > 
> > Reading my (old) internal harddrive with an external USB docking
> > station is possible without any problems, though.
> > 
> > Unfortunatelu I have no space for 1T image of that drive -- otherwise
> > I would have made an image copy and experiment with that.
> > 
> > So better ask, than sorry.... ;)
> > 
> > Is this fixable or did I lost my backups?
> > 
> Do you have access to an old kernel?
> 
> The other thing is try using gdisk (or that could be fdisk under another
> name :-( But some partitioning schemes can write a GPT with protective
> MBR - if you can find something that will take the MBR and write it as a
> GPT that might help, too.
> 
> Cheers,
> Wol
> 

Hi Wol,

thank you for your posting! :)

I switched to my new PC around 31.3.2020...
so there is no change "over the years" involved here...I think.
Where in the kernel this update is made?
I cannot remember to have configured such a thing manually...

Changing the partitiontable in any way is risky to the data 
I think...I am very unsure to do this.

I have access to an old kernel / system and can boot it.

But than I have the same problem another way around: I can
no longer access my new system ... due to the different 
sector size....

Are there any other ways to fix this problem?

Cheers!
Meino