[linux-lvm] lvm2 specificiation

[linux-lvm] lvm2 specificiation

[Vinay Srini]

Hello,

New to linux-lvm, I have been looking around to understand lvm, and have 
a few questions.

I have a requirement to mount multiple volume groups with the same name 
(VolGroup00, as that is the most popular default name), without first 
using vgrename (because something might go wrong, and I may not be able 
to restore the name back).

I tried multiple variations including chroot to mount volumegroups. 
Seems to be some conflict with device mapper (since chroot uses the same 
kernel module).

Another way was to modify and compile my own version of lvm-tools to 
give volume groups another name (alias) before mounting them, and was 
not successful.

Can someone point me in a direction that I could try? Also, have been 
looking around, and cannot find the specification for lvm2. Can I get a 
pointer to that too.

thanks,
Vinay Srini

Re: [linux-lvm] lvm2 specificiation

[Alasdair G Kergon]

On Thu, Feb 05, 2009 at 01:54:00PM -0800, Vinay Srini wrote:
> I have a requirement to mount multiple volume groups with the same name 
> (VolGroup00, as that is the most popular default name), without first 
> using vgrename (because something might go wrong, and I may not be able 
> to restore the name back).
 
It was an early design decision that every VG on a system should have a
different name.  Departures from that won't get supported - because it's so
simple to choose different names!

Alasdair
-- 
agk@redhat.com

Re: [linux-lvm] lvm2 specificiation

[Les Mikesell]

Alasdair G Kergon wrote:
> On Thu, Feb 05, 2009 at 01:54:00PM -0800, Vinay Srini wrote:
>> I have a requirement to mount multiple volume groups with the same name 
>> (VolGroup00, as that is the most popular default name), without first 
>> using vgrename (because something might go wrong, and I may not be able 
>> to restore the name back).
>  
> It was an early design decision that every VG on a system should have a
> different name.  Departures from that won't get supported - because it's so
> simple to choose different names!

How do you move drives around among machines then, if they have been 
created with the default names that will conflict?

-- 
   Les Mikesell
     lesmikesell@gmail.com

Re: [linux-lvm] lvm2 specificiation

[Vinay Srini]

Les Mikesell wrote:
> Alasdair G Kergon wrote:
>> On Thu, Feb 05, 2009 at 01:54:00PM -0800, Vinay Srini wrote:
>>> I have a requirement to mount multiple volume groups with the same 
>>> name (VolGroup00, as that is the most popular default name), without 
>>> first using vgrename (because something might go wrong, and I may not 
>>> be able to restore the name back).
>>  
>> It was an early design decision that every VG on a system should have a
>> different name.  Departures from that won't get supported - because 
>> it's so
>> simple to choose different names!
> 
> How do you move drives around among machines then, if they have been 
> created with the default names that will conflict?
> 

These are flat files mounted in a directory across the network. Which 
when accessed, gets bytes across the network. (mounted using fuse libs)

eg. if the flat file is located in /mnt/over-network/flat,
# losetup -f --show /mnt/over-network/flat
/dev/loop0

# vgscan (this will find my VolGroup00)
# .. and so on

One example is mounting virtual machine drives from the virtual server 
on to my desktop. In this case, i would like to perform some operations 
on the drive (copy from/to etc), and unmount.

Is there an RFC for the lvm design that I could read throught to better 
understand this?

Vinay.

Re: [linux-lvm] lvm2 specificiation

[Bryn M. Reeves]

Les Mikesell wrote:
> Alasdair G Kergon wrote:
>> On Thu, Feb 05, 2009 at 01:54:00PM -0800, Vinay Srini wrote:
>>> I have a requirement to mount multiple volume groups with the same 
>>> name (VolGroup00, as that is the most popular default name), without 
>>> first using vgrename (because something might go wrong, and I may not 
>>> be able to restore the name back).
>>  
>> It was an early design decision that every VG on a system should have a
>> different name.  Departures from that won't get supported - because 
>> it's so
>> simple to choose different names!
> 
> How do you move drives around among machines then, if they have been 
> created with the default names that will conflict?
> 

Using the oft-posted directions for changing the VG name and UUID.

Regards,
Bryn.

Re: [linux-lvm] lvm2 specificiation

[Stuart D. Gathman]

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Les Mikesell wrote:
>>
>> It was an early design decision that every VG on a system should have a
>> different name.  Departures from that won't get supported - because
>> it's so
>> simple to choose different names!
> How do you move drives around among machines then, if they have been
> created with the default names that will conflict?

SAN based snapshots are the legitimate reason to wish for multiple VGs
with the same name.  However, it is simpler all around if there was an
easy way to relabel SAN snapshots before the duplicate names (and VGIDs)
cause trouble.

Apart from SAN snapshots, my rule of thumb is that local fixed drives
are always called "rootvg".  All removeable, SAN, or other drives that
are likely to logically or physically move between machines get unique
VG names.  In the rare event I need to mount a rootvg from a failed
machine on a working machine (has happened only once), I boot from CD to
rename it (and the unique VGIDs make this doable).

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[linux-lvm] Re: lvm2 specificiation

[Stefan Monnier]

> How do you move drives around among machines then, if they have been created
> with the default names that will conflict?

Never use the default names?


        Stefan