Provided by: ganeti-3.1_3.1.0~rc2-2_all 
Name
ganeti-extstorage-interface - Specifications for ExtStorage providers
DESCRIPTION
The method for supporting external shared storage in Ganeti is to have an ExtStorage provider for each
external shared storage hardware type. The ExtStorage provider is a set of files (executable scripts and
text files), contained inside a directory which is named after the provider. This directory must be
present across all nodes of a nodegroup (Ganeti doesn't replicate it), in order for the provider to be
usable by Ganeti for this nodegroup (valid). The external shared storage hardware should also be
accessible by all nodes of this nodegroup too.
REFERENCE
There are eight required files: create, attach, detach, remove, grow, setinfo, verify, (executables) and
parameters.list (text file).
There are also three optional files: open, close, and snapshot (executables).
Common environment
All commands will get their input via environment variables. A common set of variables will be exported
for all commands, and some commands might have extra variables. Note that all counts are zero-based.
Since Ganeti version 2.5, the environment will be cleaned up before being passed to scripts, therefore
they will not inherit the environment in with which the ganeti node daemon was started. If you depend on
any environment variables (non-Ganeti), then you will need to define or source them appropriately.
VOL_NAME
The name of the volume. This is unique for Ganeti and it uses it to refer to a specific volume
inside the external storage. Its format is UUID.ext.diskX where UUID is produced by Ganeti and is
unique inside the Ganeti context. X is the number of the disk count.
VOL_SIZE
Available only to the create and grow scripts. The volume's size in mebibytes.
VOL_NEW_SIZE
Available only to the grow script. It declares the new size of the volume after grow (in
mebibytes). To find the amount of grow, the script should calculate the number VOL_NEW_SIZE -
VOL_SIZE.
EXTPname
Each ExtStorage parameter (see below) will be exported in its own variable, prefixed with EXTP_,
and upper-cased. For example, a fromsnap parameter will be exported as EXTP_FROMSNAP.
VOL_METADATA
Available only to the setinfo script. A string containing metadata to be associated with the
volume. Currently, Ganeti sets this value to originstname+X where X is the instance's name.
VOL_CNAME
The human-readable name of the Disk config object (optional).
VOL_UUID
The uuid of the Disk config object.
VOL_SNAPSHOT_NAME
The name of the volume's snapshot.
VOL_SNAPSHOT_SIZE
The size of the volume's snapshot.
VOL_OPEN_EXCLUSIVE
Whether the volume will be opened for exclusive access or not. This will be False (denoting
shared access) during migration.
EXECUTABLE SCRIPTS
create
The create command is used for creating a new volume inside the external storage. The VOL_NAME denotes
the volume's name, which should be unique. After creation, Ganeti will refer to this volume by this name
for all other actions.
Ganeti produces this name dynamically and ensures its uniqueness inside the Ganeti context. Therefore,
you should make sure not to provision manually additional volumes inside the external storage with this
type of name, because this will lead to conflicts and possible loss of data.
The VOL_SIZE variable denotes the size of the new volume to be created in mebibytes.
If the script ends successfully, a new volume of size VOL_SIZE should exist inside the external storage.
e.g:: a lun inside a NAS appliance.
The script returns 0 on success.
attach
This command is used in order to make an already created volume visible to the physical node which will
host the instance. This is done by mapping the already provisioned volume to a block device inside the
host node.
The VOL_NAME variable denotes the volume to be mapped.
After successful attachment the script returns to its stdout a string, which is the full path of the
block device to which the volume is mapped. e.g:: /dev/dummy1
When attach returns, this path should be a valid block device on the host node.
The attach script should be idempotent if the volume is already mapped. If the requested volume is
already mapped, then the script should just return to its stdout the path which is already mapped to.
In case the storage technology supports userspace access to volumes as well, e.g. the QEMU Hypervisor
can see an RBD volume using its embedded driver for the RBD protocol, then the provider can return extra
lines denoting the available userspace access URIs per hypervisor. The URI should be in the following
format: <hypervisor>:<uri>. For example, a RADOS provider should return kvm:rbd:<pool>/<volume name> in
the second line of stdout after the local block device path (e.g. /dev/rbd1).
So, if the access disk parameter is userspace for the ext disk template, then the QEMU command will end
up having file=<URI> in the -drive option.
In case the storage technology supports only userspace access to volumes, then the first line of stdout
should be an empty line, denoting that a local block device is not available. If neither a block device
nor a URI is returned, then Ganeti will complain.
detach
This command is used in order to unmap an already mapped volume from the host node. Detach undoes
everything attach did. This is done by unmapping the requested volume from the block device it is mapped
to.
The VOL_NAME variable denotes the volume to be unmapped.
detach doesn't affect the volume itself. It just unmaps it from the host node. The volume continues to
exist inside the external storage. It's just not accessible by the node anymore. This script doesn't
return anything to its stdout.
The detach script should be idempotent if the volume is already unmapped. If the volume is not mapped,
the script doesn't perform any action at all.
The script returns 0 on success.
remove
This command is used to remove an existing volume from the external storage. The volume is permanently
removed from inside the external storage along with all its data.
The VOL_NAME variable denotes the volume to be removed.
The script returns 0 on success.
grow
This command is used to grow an existing volume of the external storage.
The VOL_NAME variable denotes the volume to grow.
The VOL_SIZE variable denotes the current volume's size (in mebibytes). The VOL_NEW_SIZE variable
denotes the final size after the volume has been grown (in mebibytes).
The amount of grow can be easily calculated by the script and is:
grow_amount = VOL_NEW_SIZE - VOL_SIZE (in mebibytes)
Ganeti ensures that: VOL_NEW_SIZE > VOL_SIZE
If the script returns successfully, then the volume inside the external storage will have a new size of
VOL_NEW_SIZE. This isn't immediately reflected to the instance's disk. See gnt-instance grow for more
details on when the running instance becomes aware of its grown disk.
The script returns 0 on success.
setinfo
This script is used to add metadata to an existing volume. It is helpful when we need to keep an
external, Ganeti-independent mapping between instances and volumes; primarily for recovery reasons. This
is provider specific and the author of the provider chooses whether/how to implement this. You can just
exit with 0, if you do not want to implement this feature, without harming the overall functionality of
the provider.
The VOL_METADATA variable contains the metadata of the volume.
Currently, Ganeti sets this value to originstname+X where X is the instance's name.
The script returns 0 on success.
verify
The verify script is used to verify consistency of the external parameters (ext-params) (see below). The
command should take one or more arguments denoting what checks should be performed, and return a proper
exit code depending on whether the validation failed or succeeded.
Currently, the script is not invoked by Ganeti, but should be present for future use and consistency with
gnt-os-interface's verify script.
The script should return 0 on success.
snapshot
The snapshot script is used to take a snapshot of the given volume.
The VOL_SNAPSHOT_NAME and VOL_SNAPSHOT_SIZE variables contain the name and size of the snapshot we are
about to create.
Currently this operation is used only during gnt-backup export and Ganeti sets those values to
VOL_NAME.snap and VOL_SIZE respectively (see above).
The script returns 0 on success.
Please note that this script is optional and not all providers should implement it. Of course if it is
not present, instance backup export will not be supported for the given provider.
open
The open script is used to open the given volume.
This makes the volume ready for I/O.
The VOL_OPEN_EXCLUSIVE variable denotes whether the volume will be opened for exclusive access or not.
It is True by default and False (denoting shared access) during migration.
The script returns 0 on success.
Please note that this script is optional and not all providers should implement it.
close
The close script is used to close the given volume.
This disables I/O on the volume.
The script returns 0 on success.
Please note that this script is optional and not all providers should implement it.
TEXT FILES
parameters.list
This file declares the parameters supported by the ExtStorage provider, one parameter per line, with name
and description (space and/or tab separated). For example:
fromsnap Snapshot name to create the volume from
nas_ip The IP of the NAS appliance
The parameters can then be used during instance add as follows:
# gnt-instance add --disk=0:fromsnap="file_name",nas_ip="1.2.3.4" ...
EXAMPLES
In the following examples we assume that you have already installed successfully two ExtStorage
providers: pvdr1 and pvdr2
Add a new instance with a 10G first disk provided by pvdr1 and a 20G second disk provided by pvdr2:
# gnt-instance add -t ext --disk=0:size=10G,provider=pvdr1
--disk=1:size=20G,provider=pvdr2
Add a new instance with a 5G first disk provided by provider pvdr1 and also pass the prm1, prm2
parameters to the provider, with the corresponding values val1, val2:
# gnt-instance add -t ext
--disk=0:size=5G,provider=pvdr1,prm1=val1,prm2=val2
Modify an existing instance of disk type ext by adding a new 30G disk provided by provider pvdr2:
# gnt-instance modify --disk 1:add,size=30G,provider=pvdr2 <instance>
Modify an existing instance of disk type ext by adding 2 new disks, of different providers, passing one
parameter for the first one:
# gnt-instance modify --disk 2:add,size=3G,provider=pvdr1,prm1=val1
--disk 3:add,size=5G,provider=pvdr2
<instance>
NOTES
Backwards compatibility
The ExtStorage Interface was introduced in Ganeti 2.7. Ganeti 2.7 and up is compatible with the
ExtStorage Interface.
Common behaviour
All the scripts should display an usage message when called with a wrong number of arguments or when the
first argument is -h or --help.
REPORTING BUGS
Report bugs to the project's issue tracker or contact the developers using the Ganeti mailing list.
SEE ALSO
Ganeti overview and specifications: ganeti(7) (general overview), ganeti-os-interface(7) (guest OS
definitions), ganeti-extstorage-interface(7) (external storage providers).
Ganeti commands: gnt-cluster(8) (cluster-wide commands), gnt-job(8) (job-related commands), gnt-node(8)
(node-related commands), gnt-instance(8) (instance commands), gnt-os(8) (guest OS commands),
gnt-storage(8) (storage commands), gnt-group(8) (node group commands), gnt-backup(8) (instance
import/export commands), gnt-debug(8) (debug commands).
Ganeti daemons: ganeti-watcher(8) (automatic instance restarter), ganeti-cleaner(8) (job queue cleaner),
ganeti-noded(8) (node daemon), ganeti-rapi(8) (remote API daemon).
Ganeti htools: htools(1) (generic binary), hbal(1) (cluster balancer), hspace(1) (capacity calculation),
hail(1) (IAllocator plugin), hscan(1) (data gatherer from remote clusters), hinfo(1) (cluster information
printer), mon-collector(7) (data collectors interface).
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Ganeti ganeti-extstorage-interface(7)