copying lvm with the same name

[Rick Stevens]

Frank Cox wrote:
> On Wed, 18 Mar 2009 12:17:13 -0700
> Rick Stevens wrote:
> 
>> Now, back to your question.  If you REALLY want to put /dev/sdb2 into a
>> new volume group, first make sure none of its space is being used in 
>> existing LVs (check the output of "lvdisplay -vm").  If it's being used, 
>> you'll have to first shrink all the filesystems on the LV to clear the
>> space, then shrink the LV itself using "lvreduce" and specifying the
>> number of extents that are on /dev/sdb2.
> 
> I don't understand what lvdisplay -vm is telling me.
> 
> QUOTE:
> [root at mutt ~]# lvdisplay -vm
>     Finding all logical volumes
>   --- Logical volume ---
>   LV Name                /dev/VolGroup00/LogVol00
>   VG Name                VolGroup00
>   LV UUID                yFemKc-s2bo-zZC0-cc7q-50By-4jQM-G1MsQr
>   LV Write Access        read/write
>   LV Status              available
>   # open                 1
>   LV Size                277.28 GB
>   Current LE             8873
>   Segments               1
>   Allocation             inherit
>   Read ahead sectors     auto
>   - currently set to     256
>   Block device           253:0
>    
>   --- Segments ---
>   Logical extent 0 to 8872:
>     Type		linear
>     Physical volume	/dev/sdb2
>     Physical extents	0 to 8872
>    
>    
>   --- Logical volume ---
>   LV Name                /dev/VolGroup00/LogVol01
>   VG Name                VolGroup00
>   LV UUID                6UuO4G-X2dI-LirG-HvVF-zLfz-hrYW-NYZEdN
>   LV Write Access        read/write
>   LV Status              available
>   # open                 1
>   LV Size                1.94 GB
>   Current LE             62
>   Segments               1
>   Allocation             inherit
>   Read ahead sectors     auto
>   - currently set to     256
>   Block device           253:1
>    
>   --- Segments ---
>   Logical extent 0 to 61:
>     Type		linear
>     Physical volume	/dev/sdb2
>     Physical extents	8873 to 8934
>  END OF QUOTE
> 
> Notice that it's telling me about sdb2 and says nothing about sda2, which is
> where my actual "in use" volume is located.

Yeah, that is curious.  It sure looks like it picked up the correct LV
sizes, but the mapping is displaying incorrectly.  When I mentioned
making sure none of /dev/sdb2 was being used, I was referring to the
"Segments" sections.  If an LV spreads across multiple PVs, this is
where it'll be shown.  The fact you caught this indicates to me that you
actually understand it better than you think!  :-)

> 
> [root at mutt ~]# pvscan
> PV /dev/sdb2   VG VolGroup00   lvm2 [279.25 GB / 32.00 MB free]
> PV /dev/sda2   VG VolGroup00   lvm2 [465.56 GB / 32.00 MB free]
> Total: 2 [744.81 GB] / in use: 2 [744.81 GB] / in no VG: 0 [0   ]
> 
> lvdisplay doesn't appear to see sda2.
> 
> I don't know if this comes back to the fact that the volume names on both sda2
> and sdb2 are the same, so it's only showing me the first (or last) one that it
> finds?

Uh, I don't think so.  Read my comments below.

> I'm wondering if I would be best off to use fdisk to nuke the thing and carry
> on from there:
> 
> [root at mutt ~]# fdisk -l
> 
> Disk /dev/sda: 500.1 GB, 500107862016 bytes
> 255 heads, 63 sectors/track, 60801 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Disk identifier: 0x5d7711f1
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sda1   *           1          25      200781   83  Linux
> /dev/sda2              26       60801   488183220   8e  Linux LVM
> 
> Disk /dev/sdb: 300.0 GB, 300069052416 bytes
> 255 heads, 63 sectors/track, 36481 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Disk identifier: 0x00041fa1
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sdb1   *           1          25      200781   83  Linux
> /dev/sdb2              26       36481   292832820   8e  Linux LVM

Ah, HAH!  Ok, do you want to run off the 300GB drive or the 500GB drive
when you're all done?  What this is showing us now is that the LVM
that's being run now is on the 300GB drive and that is indeed /dev/sdb,
so the "lvdisplay -vm" DOES reflect reality at the moment.

Ok, so, here's what I need to know to help you sort this out:

1. Which drive do you want to be active, the 300GB or 500GB?
2. What kind of interface the drives are (IDE, SATA, SCSI)?
3. What are the drive assignments (if IDE, which is master, which is 
slave, are either or both in "cable select" mode; if SCSI, which IDs
do they occupy, etc.)

Perhaps we should take this off-list--I don't know that we want to
occupy the list's bandwidth with the back-and-forth of geting this
sorted.  When it's fixed, we could post a summary on what we did for
those who are interested.
----------------------------------------------------------------------
- Rick Stevens, Systems Engineer                      ricks at nerd.com -
- AIM/Skype: therps2        ICQ: 22643734            Yahoo: origrps2 -
-                                                                    -
-   The light at the end of the tunnel is really an oncoming train.  -
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