What can interfere with the conversion of a disk from mbr to gpt?

Question

linux

In this arch wiki article, I came across this explanation:

Remember that GPT stores a secondary table at the end of disk. This data structure consumes 33 512-byte sectors by default. MBR doesn't have a similar data structure at its end, which means that the last partition on an MBR disk sometimes extends to the very end of the disk and prevents complete conversion. If this happens to you, you must abandon the conversion, resize the final partition, or convert everything but the final partition.

1. Under what conditions does this even happen?
   
2. How to avoid this and generally make sure that the disk is 100% converted to gpt, without residual rudiments in the form of remnants of the mbr partition?
   
3. How exactly is it recommended to resize a section that interferes with the conversion? Do I understand correctly that you need to shift it from the end of the disk, or vice versa so that it takes up a small part at the end?
   
4. Will the gpt table be duplicated in this case?
   
5. What else can interfere with the complete conversion of the partition table, has anyone had such cases?
   

Answer 1

GPT occupies 33 sectors at the beginning and end of the disk.
MBR - 63 only at the beginning.
About that and the warning that if your disk is marked up to the last LBA, then there is nowhere to write the backup GPT. Your data may already be there.
You can mark partitions as you like, as long as there are at least 33 unallocated sectors at the beginning and end of LBA addressing. Better than 40 sectors - 4kb offset alignment is very useful for both SSDs and most modern HDDs.
An example of my parted /dev/sdc unit sp:

Model: ATA WDC WD20EARS-00M (scsi)
Disk /dev/sdc: 3907029168s
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:
Number Start End Size File system Name Flags
1 40s 295s 256s boot_grub bios_grub
2 296s 260231s 259936s boot boot, esp
3 260232s 27295879s 27035648s ext4 r10perf raid
4 27295880s 3907029127s 3879733248s r5stor raid

The first partition starts from sector 40, where the GPT starts
. I left 40 sectors at the end of the disk to accommodate the GPT backup.