[linux-lvm] LVM groups not visible

J.L. Blom jlblom at neuroweave.nl
Fri Nov 10 23:05:34 UTC 2006

On Fri, 2006-11-10 at 12:22 -0700, Lamont R. Peterson wrote:

> Looks like the USB device wasn't plugged in when the box was booted, perhaps?
Thanks very much for your detailed explanation.
Yes, I did plug it in after I had started 
> Standard thing to see.  It's a mostly stupid warning these days, as every 
> desktop & notebook motherboard made in the past 8 years (or so) has LBA 
> support out of the box, so it isn't an issue.  In other words, you can just 
> ignore that.

I agree. It's a very old remark. Apparently nobody bothers to remove it
when upgrading the package.
> > Warning: invalid flag 0x0000 of partition table 4 will be corrected by
> > w(rite)
> That sometimes happens when the partition table was initially created by some 
> other tool (like Windows, or Partition Magic), as they don't all do exactly 
> the same thing with some parts of it.  Given that the "offending" flag's 
> value was 0x0000, I think it be that it was just never set by the other tool.
> However, that's not why this is happening in this case (read the next bit to 
> see what's up).

> This is blank because you are trying to read a partition table from the 1st 
> partition.  You ran "fdisk /dev/sda1" not "fdisk /dev/sda" as it should have 
> been.  I hate it when I do that :) .
Yes! Sorry my own stupidity. 

> Since it's a USB disk, I would guess that it wasn't inserted when you booted 
> your box.  So, when LVM was being set up by /etc/rc.sysinit, it didn't find 
> that device.  If you did another "pvscan" after inserting the USB disk, it 
> might find it.
Well, no. When I did a pvscan it reported only the already installed
devices but pvscan -n gave what I think is the culprit:
 pvscan -n
  WARNING: only considering physical volumes in no volume group
  Couldn't find device with uuid
  No matching physical volumes found
Apparently the mentioned uuid is from the pv on the USB disk and for
some reason he cannot see it.
What would happen if I unmount the device and then do a pvscan? 
> I already covered the problem with fdisk.

> OK.  Overall, I wouldn't bother trying to use LVM with a removable drive 
> (USB/Firewire hard drives, keychain drives, etc.).  I can think of one 
> possibly viable way of doing it, but I still probably wouldn't even in that 
> case, because it wouldn't really give you any benefits.
I understand and had thought it would better to remove it.
> So, if you have already included the USB drive into your VG(s), get everything 
> plugged in, make sure pvdisplay, vgdisplay, lvscan and friends are all happy, 
> then run "pvmove /dev/sda1".  This will move any data you may have on there 
> to other drives (the one built in to your box).
But isn't that a problem as the removable disks has > 100 GB backup data
and the fixed disks together are smaller (and have > 50 % occupied)
> In this thread, everyone has been *assuming* that your USB disk is /dev/sda.  
> If your main hard drive is SATA or SCSI, it very well could be /dev/sda and 
> your USB drive could be /dev/sdb or some other device; i.e., the last letter 
> in the device name could be 'a', 'b', 'c', etc.  Run "fdisk -l" to see a list 
> of all the hard drives your system currently sees without the USB drive 
> plugged in, then plug it in and re-run "fdisk -l" and the extra one the 
> second time is your USB drive.  Make sure you use the correct device name in 
> your pvmove command.
> Once the pvmove command is finished, you can safely "redo" your USB device.  
> If it's a hard drive, format it with ext3 or reiserfs or jfs or xfs (as you 
> prefer).  If it's a flash device, I would recommend that you look at using 
> JFFS2 for the filesystem.  Either way, make sure that the "type" (i.e. System 
> ID) of the partition on your USB device is "83" (for regular Linux 
> filesystems) and not "8e" (which is for Linux LVM PVs).
My fixed disks are IDE so the USB disk is /dev/sda.
I have had a look at JFFS but haven't used it do I have to know more of
it before I can use it.
One curious point when I run fdisk -l it gives my logical volumes
as /dev/dm-(1-5) but cannot find any meaningful information (which I
think is understandable).
Lamont, thanks again for your explanation and maybe you can clarify the
pvmove in this case as I think I don't have enough diskspace for that
> np.  HTH.
> [snip]
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