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Previously, when a device was missing from a volume group or logical volume, it was impossible to add or remove tags from the logical volume. If the activation of the logical volume was based on tagging and the 'volume_list' parameter in the configuration file (lvm.conf), it would be impossible to activate a logical volume. This is an important case because it affects HA-LVM. Without the ability to add or remove tags while a device was missing, it was impossible to use RAID logical volumes with HA-LVM.
DescriptionJonathan Earl Brassow
2012-10-10 16:40:32 UTC
The --[add|del]tag arguments for vgchange and lvchange should be allowed to update metadata even when "partial".
The necessity for this is given in the upstream commit message here:
commit 3501f17fd0fcec2a1fbb8aeecf228e86ee022d99
Author: Jonathan Brassow <jbrassow>
Date: Wed Oct 10 11:33:10 2012 -0500
[lv|vg]change: Allow limited metadata changes when PVs are missing
A while back, the behavior of LVM changed from allowing metadata changes
when PVs were missing to not allowing changes. Until recently, this
change was tolerated by HA-LVM by forcing a 'vgreduce --removemissing'
before trying (again) to add tags to an LV and then activate it. LVM
mirroring requires that failed devices are removed anyway, so this was
largely harmless. However, RAID LVs do not require devices to be removed
from the array in order to be activated. In fact, in an HA-LVM
environment this would be very undesirable. Device failures in such an
environment can often be transient and it would be much better to restore
the device to the array than synchronize an entirely new device.
There are two methods that can be used to setup an HA-LVM environment:
"clvm" or "tagging". For RAID LVs, "clvm" is out of the question because
RAID LVs are not supported in clustered VGs - not even in an exclusively
activated manner. That leaves "tagging". HA-LVM uses tagging - coupled
with 'volume_list' - to ensure that only one machine can have an LV active
at a time. If updates are not allowed when a PV is missing, it is
impossible to add or remove tags to allow for activation. This removes
one of the most basic functionalities of HA-LVM - site redundancy. If
mirroring or RAID is used to replicate the storage in two data centers
and one of them goes down, a server and a storage device are lost. When
the service fails-over to the alternate site, the VG will be "partial".
Unable to add a tag to the VG/LV, the RAID device will be unable to
activate.
The solution is to allow vgchange and lvchange to alter the LVM metadata
for a limited set of options - --[add|del]tag included. The set of
allowable options are ones that do not cause changes to the DM kernel
target (like --resync would) or could alter the structure of the LV
(like allocation or conversion).
Comment 1Jonathan Earl Brassow
2012-10-10 16:45:08 UTC
The ability to use RAID LVs in an HA-LVM environment (bug 824153) has two components:
1) The LVM specific changes outlined in this bug
2) The resource-agent changes necessary in bug 824153
This bug is created to ensure that the necessary LVM changes are picked up.
Comment 2Jonathan Earl Brassow
2012-10-11 15:24:51 UTC
Unit testing performed can be found in lvm2/test/shell/*change-partial.sh.
To test this change, do the following:
1) Create volume group
2) create RAID LV (lvcreate --type raid1 -m 1 -l 2 -n $lv1 $vg)
3) deactivate LV (lvchange -an $vg/$lv1)
4) disable one of the RAID devices
5) Perform "tag" operations on LV (lvchange --addtag foo $vg/$lv1)
6) Perform "tag" operations on VG (vgchange --addtag foo $vg)
The tag operations will succeed if the change has been implemented. Otherwise, the tag operations will fail.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHBA-2013-0501.html
The --[add|del]tag arguments for vgchange and lvchange should be allowed to update metadata even when "partial". The necessity for this is given in the upstream commit message here: commit 3501f17fd0fcec2a1fbb8aeecf228e86ee022d99 Author: Jonathan Brassow <jbrassow> Date: Wed Oct 10 11:33:10 2012 -0500 [lv|vg]change: Allow limited metadata changes when PVs are missing A while back, the behavior of LVM changed from allowing metadata changes when PVs were missing to not allowing changes. Until recently, this change was tolerated by HA-LVM by forcing a 'vgreduce --removemissing' before trying (again) to add tags to an LV and then activate it. LVM mirroring requires that failed devices are removed anyway, so this was largely harmless. However, RAID LVs do not require devices to be removed from the array in order to be activated. In fact, in an HA-LVM environment this would be very undesirable. Device failures in such an environment can often be transient and it would be much better to restore the device to the array than synchronize an entirely new device. There are two methods that can be used to setup an HA-LVM environment: "clvm" or "tagging". For RAID LVs, "clvm" is out of the question because RAID LVs are not supported in clustered VGs - not even in an exclusively activated manner. That leaves "tagging". HA-LVM uses tagging - coupled with 'volume_list' - to ensure that only one machine can have an LV active at a time. If updates are not allowed when a PV is missing, it is impossible to add or remove tags to allow for activation. This removes one of the most basic functionalities of HA-LVM - site redundancy. If mirroring or RAID is used to replicate the storage in two data centers and one of them goes down, a server and a storage device are lost. When the service fails-over to the alternate site, the VG will be "partial". Unable to add a tag to the VG/LV, the RAID device will be unable to activate. The solution is to allow vgchange and lvchange to alter the LVM metadata for a limited set of options - --[add|del]tag included. The set of allowable options are ones that do not cause changes to the DM kernel target (like --resync would) or could alter the structure of the LV (like allocation or conversion).