Notice

This document is for a development version of Ceph.

# 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


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