How to safely remove rest of GTP?

[Slawa Olhovchenkov]

On Fri, Dec 30, 2016 at 10:37:10AM -0700, Ian Lepore wrote:

> On Fri, 2016-12-30 at 20:08 +0300, Andrey V. Elsukov wrote:
> > On 30.12.2016 19:46, Slawa Olhovchenkov wrote:
> > > 
> > > On Fri, Dec 30, 2016 at 07:28:19PM +0300, Andrey V. Elsukov wrote:
> > > 
> > > > 
> > > > On 30.12.2016 15:44, Slawa Olhovchenkov wrote:
> > > > > 
> > > > > How to safely remove rest of GPT?
> > > > > Disk have actual data (part of ZFS), I am don't need to destroy
> > > > > this
> > > > > data.
> > > > > 
> > > > > GEOM: da6: the primary GPT table is corrupt or invalid.
> > > > > GEOM: da6: using the secondary instead -- recovery strongly
> > > > > advised.
> > > > > GEOM: da22: the primary GPT table is corrupt or invalid.
> > > > > GEOM: da22: using the secondary instead -- recovery strongly
> > > > > advised.
> > > > > GEOM: da6: the primary GPT table is corrupt or invalid.
> > > > > GEOM: da6: using the secondary instead -- recovery strongly
> > > > > advised.
> > > > > GEOM: da22: the primary GPT table is corrupt or invalid.
> > > > > GEOM: da22: using the secondary instead -- recovery strongly
> > > > > advised.
> > > > You may try attached patch, I did only basic tests, so first try
> > > > somewhere :)
> > > What purpose of this patch?
> > In case when you have not valid primary header, `gpart destroy` will
> > not 
> > touch first two sectors. In you case you can wipe only last sector,
> > like 
> > Ian suggested, but use 'gpart destroy -F da6' instead of dd.
> > 
> 
> If you gpart destroy -F da6 won't that also clear the valid MBR at the
> start of the disk?  I think Slawa needs to preserve that.

I am don't have any partition scheme on disk -- whole disk for ZFS.
May be someone use some scheme before, on other server, before insert.
I am don't need it.

> I think it would be really useful if gpart recover could help with this
> somehow.  There is a valid mbr, and a partially-valid gpt (only the
> backup is valid).  So gpart recover should provide a way to recover the
> gpt by refreshing the primary gpt and the pbmr, or recover the mbr by
> wiping the backup gpt.  I'm not sure what the syntax would be to
> specify that, though.
> 
> This didn't used to be a problem until the changes that made the backup
> gpt get used automatically without any sysadmin intervention.

This is other case, but may be usefull too.