In some cases creating an LVM2 Physical Volume on top of a DMRaid array
reports no usage information and this partition warning:
Unable to read the contents of this file system!
Because of this some operations may be unavailable.
The cause might be a missing software package.
The following list of software packages is required for lvm2
pv file system support: lvm2.
For example on Ubuntu 14.04 LTS (with GParted built with
--enable-libparted-dmraid) create an LVM2 PV in a DMRaid array
partition. GParted uses this command:
# lvm pvcreate -M 2 /dev/mapper/isw_bacdehijbd_MyArray0p2
But LVM reports the PV having a different name:
# lvm pvs
PV VG Fmt Attr PSize PFree
/dev/disk/by-id/dm-name-isw_bacdehijbd_MyArray0p2 lvm2 a-- 1.00g 1.00g
This alternate name is loaded into the LVM2_PV_Info module cache. Hence
when GParted queries partition /dev/mapper/isw_bacdehijbd_MyArray0p2 it
has no PV information against that name and reports unknown usage.
However they are actually the same block special device; major 252,
minor 2:
# ls -l /dev/mapper/isw_bacdehijbd_MyArray0p2
brw-rw---- 1 root disk 252, 2 Jul 2 11:09 /dev/mapper/isw_bacdehijbd_MyArray0p2
# ls -l /dev/disk/by-id/dm-name-isw_bacdehijbd_MyArray0p2
lrwxrwxrwx 1 root root 10 Jul 2 11:09 /dev/disk/by-id/dm-name-isw_bacdehijbd_MyArray0p2 -> ../../dm-2
# ls -l /dev/dm-2
brw-rw---- 1 root disk 252, 2 Jul 2 11:09 /dev/dm-2
To determine if two names refer to the same block special device their
major, minor numbers need to be compared, instead of string comparing
their names.
Implement class BlockSpecial which encapsulates the name and major,
minor numbers for a block special device. Also performs comparison as
needed. See bug 767842 comments 4 and 5 for further investigation and
decision for choosing to implement a class.
Replace name strings in the LVM2_PV_Info module with BlockSpecial
objects performing correct block special device comparison.
Bug 767842 - File system usage missing when tools report alternate block
device names
ab2d4f5ee6