LVM
The backend of ceph-volume lvm is LVM, it relies heavily on the usage of
tags, which is a way for LVM to allow extending its volume metadata. These
values can later be queried against devices and it is how they get discovered
later.
Warning
These APIs are not meant to be public, but are documented so that it is clear what the tool is doing behind the scenes. Do not alter any of these values.
Tag API
The process of identifying logical volumes as part of Ceph relies on applying tags on all volumes. It follows a naming convention for the namespace that looks like:
ceph.<tag name>=<tag value>
All tags are prefixed by the ceph keyword to claim ownership of that
namespace and make it easily identifiable. This is how the OSD ID would be used
in the context of lvm tags:
ceph.osd_id=0
Metadata
The following describes all the metadata from Ceph OSDs that is stored on an LVM volume:
type
Describes if the device is an OSD or Journal, with the ability to expand to other types when supported (for example a lockbox)
Example:
ceph.type=osd
cluster_fsid
Example:
ceph.cluster_fsid=7146B649-AE00-4157-9F5D-1DBFF1D52C26
data_device
Example:
ceph.data_device=/dev/ceph/data-0
data_uuid
Example:
ceph.data_uuid=B76418EB-0024-401C-8955-AE6919D45CC3
journal_device
Example:
ceph.journal_device=/dev/ceph/journal-0
journal_uuid
Example:
ceph.journal_uuid=2070E121-C544-4F40-9571-0B7F35C6CB2B
encrypted
Example for enabled encryption with luks:
ceph.encrypted=1
When encryption is not supported or simply disabled:
ceph.encrypted=0
osd_fsid
Example:
ceph.osd_fsid=88ab9018-f84b-4d62-90b4-ce7c076728ff
osd_id
Example:
ceph.osd_id=1
block_device
Just used on bluestore backends. Captures the path to the logical volume path.
Example:
ceph.block_device=/dev/mapper/vg-block-0
block_uuid
Just used on bluestore backends. Captures either the logical volume UUID or the partition UUID.
Example:
ceph.block_uuid=E5F041BB-AAD4-48A8-B3BF-31F7AFD7D73E
db_device
Just used on bluestore backends. Captures the path to the logical volume path.
Example:
ceph.db_device=/dev/mapper/vg-db-0
db_uuid
Just used on bluestore backends. Captures either the logical volume UUID or the partition UUID.
Example:
ceph.db_uuid=F9D02CF1-31AB-4910-90A3-6A6302375525
wal_device
Just used on bluestore backends. Captures the path to the logical volume path.
Example:
ceph.wal_device=/dev/mapper/vg-wal-0
wal_uuid
Just used on bluestore backends. Captures either the logical volume UUID or the partition UUID.
Example:
ceph.wal_uuid=A58D1C68-0D6E-4CB3-8E99-B261AD47CC39
vdo
A VDO-enabled device is detected when device is getting prepared, and then
stored for later checks when activating. This affects mount options by
appending the discard mount flag, regardless of mount flags being used.
Example for an enabled VDO device:
ceph.vdo=1