rbdmap – map RBD devices at boot time¶
Synopsis¶
Description¶
rbdmap is a shell script that automates rbd map and rbd unmap
operations on one or more RBD (RADOS Block Device) images. While the script can be
run manually by the system administrator at any time, the principal use case is
automatic mapping/mounting of RBD images at boot time (and unmounting/unmapping
at shutdown), as triggered by the init system (a systemd unit file,
rbdmap.service is included with the ceph-common package for this purpose).
The script takes a single argument, which can be either “map” or “unmap”.
In either case, the script parses a configuration file (defaults to /etc/ceph/rbdmap,
but can be overridden via an environment variable RBDMAPFILE). Each line
of the configuration file corresponds to an RBD image which is to be mapped, or
unmapped.
The configuration file format is:
IMAGESPEC RBDOPTS
where IMAGESPEC should be specified as POOLNAME/IMAGENAME (the pool
name, a forward slash, and the image name), or merely IMAGENAME, in which
case the POOLNAME defaults to “rbd”. RBDOPTS is an optional list of
parameters to be passed to the underlying rbd map command. These parameters
and their values should be specified as a comma-separated string:
PARAM1=VAL1,PARAM2=VAL2,...,PARAMN=VALN
This will cause the script to issue an rbd map command like the following:
rbd map POOLNAME/IMAGENAME --PARAM1 VAL1 --PARAM2 VAL2
(See the rbd manpage for a full list of possible options.)
For parameters and values which contain commas or equality signs, a simple
apostrophe can be used to prevent replacing them.
When run as rbdmap map, the script parses the configuration file, and for
each RBD image specified attempts to first map the image (using the rbd map
command) and, second, to mount the image.
When run as rbdmap unmap, images listed in the configuration file will
be unmounted and unmapped.
rbdmap unmap-all attempts to unmount and subsequently unmap all currently
mapped RBD images, regardless of whether or not they are listed in the
configuration file.
If 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, /dev/rbd/POOLNAME/IMAGENAME, pointing to the real mapped
device.
In order for mounting/unmounting to succeed, the friendly device name must
have a corresponding entry in /etc/fstab.
When writing /etc/fstab entries for RBD images, it’s 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 in question even
exists. (Since rbdmap.service
executes a shell script, it is typically triggered quite late in the boot
sequence.)
Examples¶
Example /etc/ceph/rbdmap for three RBD images called “bar1”, “bar2” and “bar3”,
which are in pool “foopool”:
foopool/bar1 id=admin,keyring=/etc/ceph/ceph.client.admin.keyring
foopool/bar2 id=admin,keyring=/etc/ceph/ceph.client.admin.keyring
foopool/bar3 id=admin,keyring=/etc/ceph/ceph.client.admin.keyring,options='lock_on_read,queue_depth=1024'
Each line in the file contains two strings: the image spec and the options to
be passed to rbd map. These two lines get transformed into the following
commands:
rbd map foopool/bar1 --id admin --keyring /etc/ceph/ceph.client.admin.keyring
rbd map foopool/bar2 --id admin --keyring /etc/ceph/ceph.client.admin.keyring
rbd map foopool/bar2 --id admin --keyring /etc/ceph/ceph.client.admin.keyring --options lock_on_read,queue_depth=1024
If the images had XFS file systems on them, the corresponding /etc/fstab
entries might look like this:
/dev/rbd/foopool/bar1 /mnt/bar1 xfs noauto 0 0
/dev/rbd/foopool/bar2 /mnt/bar2 xfs noauto 0 0
/dev/rbd/foopool/bar3 /mnt/bar3 xfs noauto 0 0
After creating the images and populating the /etc/ceph/rbdmap file, making
the images get automatically mapped and mounted at boot is just a matter of
enabling that unit:
systemctl enable rbdmap.service
Options¶
None
Availability¶
rbdmap is part of Ceph, a massively scalable, open-source, distributed storage system. Please refer to the Ceph documentation at http://ceph.com/docs for more information.
