[dm-devel] partx fails 4096 block size

Bryn M. Reeves bmr at redhat.com
Tue Sep 16 08:52:34 UTC 2014

On Mon, Sep 15, 2014 at 02:48:23PM -0500, Ross Anderson wrote:
> I'd appreciate any help in troubleshooting this. Quiet frustrating not being
> able to use mpath on 4k blocks.

Doesn't seem related to sector size.
> http://pastebin.com/EbTMXdvE

> ###partx -a-v
> partition: none, disk: /dev/dm-0, lower: 0, upper: 0
> /dev/dm-0: partition table type 'gpt' detected
> partx: /dev/dm-0: adding partition #1 failed: Invalid argument

partx is trying to call a BLKPG partition management ioctl on a
device-mapper device. Since dm devices are not partitionable it
fails with EINVAL.

> partx: /dev/dm-0: adding partition #2 failed: Invalid argument
> partx: /dev/dm-0: error adding partitions 1-2

The partx program comes from the util-linux package:

$ qwhich partx

You're probably looking for kpartx which is part of multipath-tools. On
Red Hat distros it's in a separate sub-package named kpartx:

$ qwhich kpartx

The kpartx command reads partition data from the disk and creates
device-mapper linear maps corresponding to each discovered partition.
This allows you to access the partitions on a device-mapper device as
separate dm devices (e.g. you'd get devices with paths like
'/dev/mapper/dm-0p1' or whatever depending on the -p switch given).

Most distros today will automatically run kpartx when new multipath
devices appear or when they change so you shouldn't need to run it
manually all the time.


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