[linux-lvm] Difference in LVM and LVM2 and their strength/weakness

[Alex Chen]

Heinz, thanks for the information/
 
The main intention of our interest of LIME to use it for snapshots.
I am told that it is a very quick way to make backups.  Is that true? Is there any measuring number for this?
 
>From the recent discussion on snapshots, it seems there are still some issues, and even a kernel patch.
Does RHEL 4 contain such patch?  Or is there a downloadable patch if we buy one?
 
>From what I've read from the Web regarding LIME is that LVM1 is a read/only while LVM2 is read/write.
The read/only mode, if I understand correctly, is that the PE where the data resides is first copied to an exception table, (is this the COW table?)
before the destination PE is changed.  Is this correct?  If so, does the copy involves actual data movement or only a manipulation of
of the FAT table?  
The LVM2's read/write mode seems to simply mark the PE in the snapshot but the change is not copied from the changed PE to the snapshot, right?
 
In either way, the snapshot seems to be keeping tracks of only the changes, i.e. delta.  Doe we need to first create a full copy of the file system as the base, or we only need to keep the deltas, if we want to use snapshot for system backups?
 
Sorry of all the questions, some of them may be pretty basic or ignorant.  If you feel I should get the answers from other sources, I would really apprecaite it if you can give me the pointer.
 
Alex 

________________________________

From: linux-lvm-bounces at redhat.com on behalf of Heinz Mauelshagen
Sent: Sat 1/21/2006 09:08
To: LVM general discussion and development
Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness



On Fri, Jan 20, 2006 at 05:54:12PM -0800, Alex Chen wrote:
> Greetings,

Hi.

>
>   I am tasked to investigate the differences between LVM and LVM2.  I am
> new to LVM so it would be greatly appreciated if someone can explain or
> point me to the right direction for the following questions:
>
> 
>
> 1.    What does LVM2 have that is not available in LVM?

It has command line extensions beyond lvm (eg, vgs, lvs, pvs commands).

It's configurable in various regards (eg, device name filters)

The limits of 256 grand total logical volumes and ~64k extents per logical
volume are gone.

Logical volume snapshots are asynchronous rather than synchronuous
and gain better performance.

pvmove (online data relocation) is based on temporary, restartable mirrors
which wasn't the case in LVM1.


> Or is it a
> only better architectured implementation of LVM?

I'ld not say 'only', but yes, it is :)


> 2.    Which version of Red Hat enterprise system uses which LVM?  And
> does the user need to do any configuration during installation?

RHEL3 comes with LVM, RHEL4 with LVM2.

> 3.    If LVM2 is definitely better than LVM, how stable is it?

It is stable with the exception of rare snapshot issues,
we're fixing right now.

>
> 
>
> Thanks.
>
> Alex
>

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--

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Red Hat GmbH
Consulting Development Engineer                   Am Sonnenhang 11
Cluster and Storage Development                   56242 Marienrachdorf
                                                  Germany
Mauelshagen at RedHat.com                            +49 2626 141200
                                                       FAX 924446
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