UFS mbr to GPT

[SingerMan]

I'm wondering whether it is useful to zero out the first 512 before changing a disk from mbr to gpt? (I’ve changed from mbr to GPT before but without zeroing.)

Of course, I’m thinking that, even with the GPT’s backup sector this might help prevent any future errors on discs that have seen considerable partition changing – anyone do this?

 

[TracyTiger]

I'm wondering whether it is useful to zero out the first 512 before changing a disk from mbr to gpt? (I’ve changed from mbr to GPT before but without zeroing.)

In the past when I've had a (re-)partitioning issue (MBR) with a tool I've found that zeroing out the first portion (I use 1MB) fixes the issue right away and I can then proceed without problems. I don't automatically zero out the first part of the disk as it is often or usually not needed. Zeroing may be a good general practice however.

My understanding is that zeroing the first part of a disk causes the partitioning tool to not guess wrong about the disk partitioning.

It sounds like you're aware that zeroing the beginning of the disk does not erase any GPT partitioning information at the end of the disk.

EDIT: I should explain that I often write random bytes to disks in preparation for encryption. This random data can confuse disk tools. Most people would not need to zero the first part of the disk as they are probably not writing random data there but zeroing shouldn't hurt anything.

 

[Emrion]

There's nothing to do when you change from MBR to GPT. The reverse may be not true, depending the tool you use.

See: https://en.wikipedia.org/wiki/GUID_Partition_Table

 

[SingerMan]

Yes Thanks to both of you. I know you don't have to zero out the first part of the disk when changing to the gpt table. But, as I suggested above this disk had undergone a lot of partition changing in past two years mbr -- ntfs - - ufs -- and a brief stint with LVM, and so I thought I go the extra mile and clear it thoroughly. I was simply curious to see if anyone was inclined to do the same. At any rate, its done now. It's a gpt disk with a new filesystem and new data. Thanks

 

[Emrion]

As you can see in the posted link, GPT installs a "protective MBR" on the first sector. So it takes over that part of the disk. But, if you imagine a MBR partitioning tool that is not GPT-aware operating on a previous GPT scheme, it will probably leave the main GPT header (at least) and both the backup header and partition table at the end of the disk. That may cause trouble.

I got problems with a ZFS partition that said, but it was a very particular case. I did zero all the disk (there was a more efficient solution, I just didn't know). Zeroing is when you encounter a problem you can't overcome. An answer to despair.