LVM How-To by Lennart

Wed Jan 17 17:09:28 UTC 2007

On Tuesday 16 January 2007 23:50, Tim Writer wrote:

Hello Tim

I know top posting is frowned on but no need to make you chase through the 
message for this. Thanks for the additional comments and examples, I hope 
that I can start to use the proper terms for working with LVM Groups.  Now 
that I have an idea what this system is all about, the HOW-TO should make 
much more sense.  It is just so long and detailed that I really got lost 
before the concepts sank in. Then any Linux documentation that is 4 years old 
is kinda suspect in my mind.

After I installed this new drive on this computer [not my Mythtv backend], I 
was tempted to make 3 small Primary partions for distro /boot use and one 
large Vol Group, but I chickened out, not knowing what I was getting into.

Now that I have your example, I see that is what I should have done.  During 
the day, I'll consider re-doing this drive before I put any more work on it.
s

Again thanks and for saving Lennart a bunch of typing, altho he might just 
pipe up anyway :-)

I am hoping that this ends this thread, but these 77 year old grey cells 
aren't so nimble anymore.

Cheers

> Merv Curley <mervc-MwcKTmeKVNQ at public.gmane.org> writes:
> > On Monday 15 January 2007 16:18, Lennart Sorensen wrote:
> > > On Fri, Jan 12, 2007 at 08:09:15PM -0500, Merv Curley wrote:
> > > > Thanks for the instructions Lennart. From what stuck in the grey
> > > > cells from the HOW-TO,  it seemed to make sense.  I assume that
> > > > somewhere in the second stage I format the 'newdisk' with ext3 to
> > > > match the present part of the logical volume?
> > >
> > > No.  You are extending an existing filesystem I imagine.  If you don't
> > > want to expand an existing logical volume, you can create a new logical
> > > volume with lvcreate and format that afterwards.
> >
> > hda on the Myth system, has a primary partition for /boot, a VolumeGroup
> > [rootvg]  for the  Myth install  / and the swap;  and a VolumeGroup for
> > Myth Data [videovg].  I have a 320 GB drive [hdb] that I thought could
> > extend the videovg group.
>
> You can. Once you have extended it you have a choice. You can extend
> existing logical volumes (using lvextend) or you can create new logical
> volumes. New logical volumes would required to create file system on them
> before mounting. Existing logical volumes likely already have a file system
> which you can simply resize (e.g. using resize2fs) once you have extended
> the volume using lvextend.
>
> You complained about the LVM HOWTO but it's actually comprehensive. I think
> it would be a good idea for you to spend some more time with it, perhaps on
> an experimental system, to be sure you understand the concepts.
>
> > > The vgdisplay should show how many free extents are unused (not used by
> > > any logical volume).  That is how many extents you can potentially add
> > > to any existing logical volume.
> >
> > Well it seems that vgdisplay didn't return what it should have because I
> > didn't use the  VolumeGroup name.  I just tried again and
> >
> >  vgdisplay videovg     [now sez among other things]
> >
> > Max PV   0  0     Cur PV  1   1      Act PV  1  1
> > VG size 225.88   PE Size 32 MB
> > Total PE 7228> >> not VMS.  It's not MVS.  All of those systems had 
special portions of
> >> filenames known as an "extension."  Unix doesn't do that.)
> > Alloc PE/Size  7227 / 225.88
> > Free PE/Size  1 / 32 MB
>
> This is before running vgextend, correct? You only have one PV (physical
> disk partition) and 1 free extent (block of 32MB available for use by LVM).
> You need to use pvcreate to prepare your new disk for use with LVM and add
> that PV to your existing volume group using vgextend. At that point, you
> should have free extents.
>
> > Is that better?
>
> No. See above.
>
> > How many free extents are there, just 1?
>
> Yes.
>
> > Is this second drive going to be videolv02 for mounting purposes in fstab
> > and a part of the 'videovg group?
>
> Absolutely not. When using LVM, you don't mount (physical) drives or
> partitions, you mount logical volumes. The purpose of LVM is to provide a
> layer between the file system and physical disks. It allows you to resize
> your logical disks (logical volumes) by adding and removing physical disk
> resources. You can then grow and shrink file systems without needing to
> backup and restore them.
>
> Let me give you a concrete example. My laptop has a single physical
> disk. It has four physical partitions: 8GB for XP (yuck!), 512MB for the
> laptop diagnostics, 256MB for /boot, and the remaining 25GB as a single PV
> for LVM.
>
> The PV comprises (is allocated to) a single volume group, vg0. Within vg0,
> I have the following logival volumes:
>
>     /dev/vg0/ub606_root
>     /dev/vg0/ub606_usr
>     /dev/vg0/ub606_var
>     /dev/vg0/home
>     /dev/vg0/ub610_root
>     /dev/vg0/ub610_usr
>     /dev/vg0/ub610_var
>
> When running Ubuntu 6.10, I have the following mounts:
>
>     /dev/vg0/ub610_root on /
>     /dev/vg0/ub610_usr on /usr
>     /dev/vg0/ub610_var on /var
>     /dev/hda3 on /boot type
>     /dev/vg0/home on /home type
>
> I have free space in vg0, as you will have after you extend it with
> pvcreate and vgextend. I can add some of that free space to /home as
> follows:
>
>     umount /home
>     lvextend -L +4G /dev/vg0/home
>     resize2fs /dev/vg0/home
>     mount /home
>
> At this point, I'll have an additional 4GB of usable space in /home. Note
> that I didn't need to backup and restore /home, and I didn't need to make a
> new file system.
>
> [snip]
>s

> Hope this helps,

-- 
Merv Curley
Toronto, Ont. Can

SuSE 10.2 Linux    
Desktop  KDE 3.5.5    KMail 1.9.5

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