[GTALUG] MBR and GTP Drives

[Lennart Sorensen]

On Tue, Oct 10, 2017 at 11:41:01PM -0400, Scott Sullivan via talk wrote:
> Wat?! ((*runs to wikipedia*))... Okay then.
> 
> I wonder under what conditions that secondary table is used. I've never had
> a front wiped disk continue to report a table afterwards. I see it mentions
> CRC checks, so maybe only when there is corporation in first table? A
> question for source code reading on another day.

The second copy us a backup in case the first gets corrupted.  Some tools
will notice it and ask if you want to restore the primary from the backup,
which means not wiping the backup makes some tools think your disk should
be GPT but something corrupted it.

> Anyways I haven't had to pull this sucker out in a few years...
> 
> dd if=/dev/zero of=$YOUR_DEV bs=512 seek=$(( $(blockdev --getsz $YOUR_DEV) -
> 34 )) count=34 #adjust bs=4K for advanced format disks.
> 
> Mostly only needed it for drives with dmraid, which stores it's config at
> the end of disks. Usually found on drives pulled from enterprise HP or DELL
> servers and/or the odd workstation.
> 
> Thankfully in most cases, I'm installing a new GPT partition tables, so it
> would be reasonable assumption the backup would be over written.

gdisk has a nice 'zap' option that removes GPT from the disk.

And yes creating a new GPT would certainly overwrite the old one.
Only a problem if changing a disk from GPT to MBR.

-- 
Len Sorensen