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Old 12-14-2009, 04:02 PM   #1
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device-mapper error running kpartx on a LVM

Hello, I'm hoping this explanation will have everything needed, just let me know what other info I need to gather.

-CentOS 5.4
-Kernel 2.6.18-164.el5xen

I use Xen to host a Windows virtual.
I have 3 volume groups configured, one for the Host (CentOS), for the guest OS setup (Windows Server 2008) and one for the data storage. The data LV is added to the Windows guest for access. Both the data and guest LVs are formatted NTFS.

I've got installed and working ntfs-3g to allow me to mount the NTFS LVs. I'm using kpartx to create a map for the LV partitions. Last week I was able to mount the guest's LV (read only to avoid issues) and browse the file system. Today, I wanted to take a backup so I tried to mount it again and I am receiving the following error:

#kpartx -av /dev/Guest/Server2008
device-mapper: reload ioctl failed: Invalid arguement
add map Server2008p1 : 0 92327928 linear /dev/Guest/Server2008 2048

#tail /var/log/messages
Dec 14 15:56:54 Virt-84 kernel: device-mapper: table: device /dev/Guest/Server2008 too small for target
Dec 14 15:56:54 Virt-84 kernel: device-mapper: table: 253:8: linear: dm-linear: Device lookup failed
Dec 14 15:56:54 Virt-84 kernel: device-mapper: ioctl: error adding target to table

Here's the kicker, I am able to run kpartx on the LV for the Data storage, and mount it read only via ntfs-3g afterwards without issue. I can't think of anything that's changed with the Guest LV that would affect this. Any ideas?

Old 12-15-2009, 03:24 PM   #2
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I've been reviewing my notes for what I had set up on this server.

I think I may have found something applicable. I successfully mounted the NTFS guest LV once before I needed to shrink the LV. I first shrank the partition from within the Guest, and then used the system-config-lvm GUI to shrink the LV. Could this have caused the issue?
Old 12-15-2009, 04:13 PM   #3
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Shrinking the volume is what caused the issue. Once I restored it to the original size, kpartx was able to map a device without issue.

Now if anyone can answer this question:
The filesystem was shrank first, then the logical volume, and everything except kpartx continued to work. Did I miss a step in shrinking the volume? I can see the need to shrink a LV in the future, and would like to make sure I do it correctly. But overall *yay*, it's fixed.


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