does creation of volume group destroys data on disk?

does creation of volume group destroys data on disk?

Post by Gerald Geudtne » Fri, 03 Dec 1999 04:00:00



Hello to all :-)

In a 4.?.? PowerPC machine one of the two installed hard disks stopped
working. My problem now is to get access to the data of the other disk.
So I connected the "good" disk to a 3.2.5 RS/6000 machine. But when I
use lspv I get the message "... is not assigned to a volume group."
(Which makes sense to me because I think the disk was not in its own VG)
It would be no problem for me to create a new VG for that disk but what
happens than to the data on the disk?
Has anyone maybe some hints or suggestions for me?

Many thanks in advance

Gerald

 
 
 

does creation of volume group destroys data on disk?

Post by Matthew Land » Fri, 03 Dec 1999 04:00:00



> Hello to all :-)

> In a 4.?.? PowerPC machine one of the two installed hard disks stopped
> working. My problem now is to get access to the data of the other disk.
> So I connected the "good" disk to a 3.2.5 RS/6000 machine. But when I
> use lspv I get the message "... is not assigned to a volume group."
> (Which makes sense to me because I think the disk was not in its own VG)
> It would be no problem for me to create a new VG for that disk but what
> happens than to the data on the disk?
> Has anyone maybe some hints or suggestions for me?

> Many thanks in advance

> Gerald

Creating a new VG will destroy the data.  Try to import it first.  If
there is a VG on that disk, the import should work.  

importvg -y testdatavg hdiskX

You can name the VG anything you want, I just named it "testdatavg".  The
name has to be unique.

Once imported you can run:

lsvg testdatavg
  and
lsvg -l testdatavg

To see what might be on that vg

 - Matt

--

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does creation of volume group destroys data on disk?

Post by John McQu » Sat, 04 Dec 1999 04:00:00


Running mkvg does not delete data on the disk. In the past I've used this
technique to take broken mirror offline copies of VGs. To access the data on
the disk you need to know where on the disk the data was. This involves
generating PP maps then using these to recreate LVs in the new VGs.
This might not help you in this circumstance unless you regularly regenerate
sets of map files.

You don't actually say if the disk is just part of the VG or a full mirror of
the other disk. If it isn't a full copy then I don't think the importvg will
work.

Bottom line is nothing is ever actually deleted it's only really gone when
something new overwrites it.

Good Luck

John



> > Hello to all :-)

> > In a 4.?.? PowerPC machine one of the two installed hard disks stopped
> > working. My problem now is to get access to the data of the other disk.
> > So I connected the "good" disk to a 3.2.5 RS/6000 machine. But when I
> > use lspv I get the message "... is not assigned to a volume group."
> > (Which makes sense to me because I think the disk was not in its own VG)
> > It would be no problem for me to create a new VG for that disk but what
> > happens than to the data on the disk?
> > Has anyone maybe some hints or suggestions for me?

> > Many thanks in advance

> > Gerald

> Creating a new VG will destroy the data.  Try to import it first.  If
> there is a VG on that disk, the import should work.

> importvg -y testdatavg hdiskX

> You can name the VG anything you want, I just named it "testdatavg".  The
> name has to be unique.

> Once imported you can run:

> lsvg testdatavg
>   and
> lsvg -l testdatavg

> To see what might be on that vg

>  - Matt

> --

>   AIX and HACMP Certified Specialist   | |  / \ |\| |  \. ,_|  ` o O '
>   / Comments, views, and opinions \    | |_/ ^ \|   | ) | |       x
>   \ are mine alone, not IBM's.    /    |___|/~\_\_|\|__/|_|     \___/

 
 
 

does creation of volume group destroys data on disk?

Post by Matthew Land » Sat, 04 Dec 1999 04:00:00




> Running mkvg does not delete data on the disk. In the past I've used this
> technique to take broken mirror offline copies of VGs. To access the data on
> the disk you need to know where on the disk the data was. This involves
> generating PP maps then using these to recreate LVs in the new VGs.
> This might not help you in this circumstance unless you regularly regenerate
> sets of map files.

> You don't actually say if the disk is just part of the VG or a full mirror of
> the other disk. If it isn't a full copy then I don't think the importvg will
> work.

> Bottom line is nothing is ever actually deleted it's only really gone when
> something new overwrites it.

> Good Luck

> John

Absolutely right.  However, to most laymen admins, overwritting the LVCB,
VGDA, VGSA etc is in essance causing the data to be lost.  There are
always methods to get data back if it has not been explicitly changed,
erased, etc.  If you doubt this, talk to the FBI.  I'm sure they have
a method or two you don't know about.  

So my responses are geared towards the questions asked.

If I do this, will I lose data:  Yes... (it will be there but NOT accessable
                                         by normal means, so unless you know
                                         what you are doing, it is lost)

I have DONE this, HAVE I lost data: No.  There are methods to help recover
                                    data from a disk whose control blocks
                                    have been accidently changed.  But
                                    recovery isn't guaranteed and it can be a
pain.

I should have stated the ()'d part in my message, I just don't like to
leave it open for people to think it's ok to shoot themselves in the
foot.

 - Matt

--

  AIX and HACMP Certified Specialist   | |  / \ |\| |  \. ,_|  ` o O '
  / Comments, views, and opinions \    | |_/ ^ \|   | ) | |       x    
  \ are mine alone, not IBM's.    /    |___|/~\_\_|\|__/|_|     \___/

 
 
 

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