Re: cloning a disk

On 2026-08-08 14:41, Stefan Monnier wrote:
>> root@melon:~# fdisk -l
>> Disk /dev/sdb: 111.79 GiB, 120034123776 bytes, 234441648 sectors
> [...]
>> GPT PMBR size mismatch (234441647 != 468862127) will be corrected by 
>> write.
>> The backup GPT table is corrupt, but the primary appears OK, so that 
>> will
>> be used.
>> The backup GPT table is not on the end of the device.
> [...]
>> Disk /dev/sdg: 223.57 GiB, 240057409536 bytes, 468862128 sectors
> [...]
>> I always thought the GPT error message was about the small OS drive 
>> but
>> I disconnected the 3TB drive and commented out its fstab entry and 
>> rebooted
> 
> The GPT partitioning format keeps 2 copies of the table of partitions: 
> one
> at the beginning of the drive and one at the end, and also the info it
> keeps includes the size of the drive.  So when you clone to
> a differently-sized drive, the 2nd (aka "backup") is inevitably
> lost/misplaced.  This is normal.
> 
> Notice how the "size mismatch (234441647 != 468862127)" mentions 
> exactly
> (well, off-by-one) the sizes of your two drives.
> 
> 
> === Stefan

This is with only the 111GB disk connected.
root@melon:~# fdisk -l
Disk /dev/sda: 111.79 GiB, 120034123776 bytes, 234441648 sectors
Disk model: CT120BX500SSD1
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: D97B2271-48BB-4988-BEFA-5153C05D7C94

Device         Start       End   Sectors   Size Type
/dev/sda1       2048   2000895   1998848   976M EFI System
/dev/sda2    2000896 222339071 220338176 105.1G Linux filesystem
/dev/sda3  222339072 234440703  12101632   5.8G Linux swap
root@melon:~#
-------
This is with only the 2.73TB and the 111GB disk connected.
root@melon:~# fdisk -l
Disk /dev/sdb: 111.79 GiB, 120034123776 bytes, 234441648 sectors
Disk model: CT120BX500SSD1
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: D97B2271-48BB-4988-BEFA-5153C05D7C94

Device         Start       End   Sectors   Size Type
/dev/sdb1       2048   2000895   1998848   976M EFI System
/dev/sdb2    2000896 222339071 220338176 105.1G Linux filesystem
/dev/sdb3  222339072 234440703  12101632   5.8G Linux swap
The backup GPT table is corrupt, but the primary appears OK, so that 
will be used.

### (^^^^^^^ I always thought that this message was about the 111GB disk 
but now I think it is the fdisk reading first the partition/GPT table of 
the 2.73TB disk)

Disk /dev/sda: 2.73 TiB, 3000592982016 bytes, 5860533168 sectors
Disk model: ST3000NM0005-1V4
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: F6A1B30E-8495-8F4B-B53D-4D80D5C28C81

Device     Start        End    Sectors  Size Type
/dev/sda1   2048 5860532223 5860530176  2.7T Linux filesystem
root@melon:~#

So now I've diverted from the original "cloning a disk" question and 
I've other issues to do with understanding the GPT of disks.
I'm not understanding if the backup GPT Header is on the primary 
partition or not.
Perhaps I should have used gdisk instead of fdisk to partition the 2.7TB 
disk?
I'm not knowing if after making the GPT table with fdisk then making 1 
primary partition on the 2.7TB disk I wrote over the GPT Backup Header.

mick