Dne 23.6.2016 v 18:35 Chris Friesen napsal(a):
On 06/23/2016 02:34 AM, Zdenek Kabelac wrote:
Dne 22.6.2016 v 16:52 Chris Friesen napsal(a):
On 06/22/2016 03:23 AM, Zdenek Kabelac wrote:
Dne 21.6.2016 v 17:22 Chris Friesen napsal(a):
I'm using the stock CentOS7 version, I think.
LVM version: 2.02.130(2)-RHEL7 (2015-12-01)
Library version: 1.02.107-RHEL7 (2015-12-01)
Driver version: 4.33.0
So are you saying that nobody should run "vgscan --mknodes" on a system
where
udev is managing the symlinks?
Yes - on such system this command should be used only in case of 'emergency',
udev doesn't work properly and you need links.
The links however will not be known to udev and likely whole system is
going to be crashing soon or is misconfigured in major way.
Okay, I'll see if I can get the call to vgscan removed. But even so wouldn't
it make sense to have vgscan use the same logic as udev in terms of what
symlinks to make and where to make them to?
It *IS* using same logic.
If the link is not there - the bug is in your udev rules.
When udev is properly configured, vgscan should not show missing link.
It doesn't seem to work this way in practice on a stock CentOS system. Here's
the sequence:
1) create a volume group:
"vgcreate chris-volumes /dev/loop2"
At this point there is no /dev/chris-volumes directory.
ONLY active volume do have links
Never ever there is supposed to be directory entry for VG without any active LV.
There is not a term 'active VG' as such - it always is in connection with
active LV - thus directory without any active LV inside is pure bug - if you
see it - report it as regular BZ..
2) Create a thin pool in the volume group:
"lvcreate -L 1.8GB -T chris-volumes/chris-volumes-pool"
Now udev creates a /dev/chris-volumes directory with a link for the thin pool:
[root@centos7 centos]# ls -l /dev/chris-volumes
total 0
lrwxrwxrwx. 1 root root 7 Jun 23 12:22 chris-volumes-pool -> ../dm-9
3) Create a thin volume in the thin pool:
"lvcreate -V1G -T chris-volumes/chris-volumes-pool -n thinvolume"
Now the link for the thin pool itself has disappeared:
[root@centos7 centos]# ls -l /dev/chris-volumes
total 0
lrwxrwxrwx. 1 root root 8 Jun 23 12:23 thinvolume -> ../dm-11
(At this point /dev/mapper/chris--volumes-chris--volumes--pool-tpool points to
dm-9 and /dev/mapper/chris--volumes-chris--volumes--pool points to dm-10.)
correct
4) If I run "vgscan --mknodes", it re-creates the thin pool link, but pointing
to the /dev/mapper name instead of directly to the /dev/dm-*. Also, it's
indirectly pointing to /dev/dm-10 where before it was pointing to /dev/dm-9:
Only 'final' resolving device does matter.
if link is /dev/vg/lv -> /dev/mapper/vg-lv -> /dev/dm-XXX
or /dev/vg/lv -> /dev/dm-XXX - it does not matter.
There are some 'tricks' related to thin-pool maintainance.
Unused thin-pool is 'public' LV - has /dev/vg/lv link.
Used thin-pool by lvm2 is 'private' LV - doesn't have /dev/vg/lv link.
All device should always have entry in /dev/mapper/ - either links
to real devices or direct nodes (on older systems)
lvm2 users are always supposed to use ONLY /dev/vg/lv devices for access.
[root@centos7 centos]# vgscan --mknodes
Configuration setting "snapshot_autoextend_percent" invalid. It's not part
of any section.
Configuration setting "snapshot_autoextend_threshold" invalid. It's not part
of any section.
fix your lvm.conf (uncomment sections)
Reading all physical volumes. This may take a while...
Found volume group "chris-volumes" using metadata type lvm2
Found volume group "centos" using metadata type lvm2
Found volume group "cinder-volumes" using metadata type lvm2
The link /dev/chris-volumes/chris-volumes-pool should have been created by
Ok - there seems to be internal bug in lvm2 - which incorrectly hints
link creation for this case.
There should not have been /dev/vg/pool link - this is correctly marked
for udev - but incorrectly for udev validation.
However the bug is actually not so much important - it just links
to 'wrapper' device - and eventually we will resolve the problem even without
this extra device in table.
Regards
Zdenek
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