rbdmap service

The systemd unit file, rbdmap.service, is included with the ceph-common package. The rbdmap.service unit runs the rbdmap shell script. This script automates the mapping and unmapping of RADOS Block Devices (RBD) for one or more RBD images.

The rbdmap script can be ran manually at any time, but the typical use case is to automatically mount RBD images at boot time, and unmount at shutdown. The script takes a single argument, which can be either map, for mounting or unmap, for unmounting RBD images. The script parses a configuration file, the default is /etc/ceph/rbdmap, but can be overridden using an environment variable called RBDMAPFILE. Each line of the configuration file corresponds to an RBD image.

The format of the configuration file format is as follows:

IMAGE_SPEC RBD_OPTS

Where IMAGE_SPEC specifies the POOL_NAME / IMAGE_NAME, or just the IMAGE_NAME, in which case the POOL_NAME defaults to rbd. The RBD_OPTS is an optional list of options to be passed to the underlying rbd map command. These parameters and their values should be specified as a comma-separated string:

OPT1=VAL1,OPT2=VAL2,...,OPT_N=VAL_N

This will cause the script to issue an rbd map command like the following:

Syntax

rbd map POOL_NAME/IMAGE_NAME --OPT1 VAL1 --OPT2 VAL2

When successful, the rbd map operation maps the image to a /dev/rbdX device, at which point a udev rule is triggered to create a friendly device name symlink, for example, /dev/rbd/POOL_NAME/IMAGE_NAME, pointing to the real mapped device. For mounting or unmounting to succeed, the friendly device name must have a corresponding entry in /etc/fstab file. When writing /etc/fstab entries for RBD images, it is a good idea to specify the noauto or nofail mount option. This prevents the init system from trying to mount the device too early, before the device exists.