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Background |
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========== |
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DRBD is currently the only shared storage backend supported by Ganeti. |
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DRBD offers the advantages of high availability while running on |
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commodity hardware at the cost of high network I/O for block-level |
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Use cases |
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We consider the following use cases: |
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- A virtualization cluster with FibreChannel shared storage, mapping at |
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storage. |
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- Introduction of a shared file storage disk template for use with networked |
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filesystems. |
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- Introduction of shared block device disk template with device |
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- Introduction of a shared block device disk template with device
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adoption. |
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- Introduction of an External Storage Interface.
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- Introduction of the External Storage Interface.
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Additionally, mid- to long-term goals include: |
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- The device will be available with the same path under all nodes in the |
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node group. |
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Introduction of an External Storage Interface
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Introduction of the External Storage Interface
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============================================== |
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Overview |
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-------- |
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- Grow a disk |
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- Attach a disk to a given node |
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- Detach a disk from a given node |
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- SetInfo to a disk (add metadata) |
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- Verify its supported parameters |
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The proposed ExtStorage interface borrows heavily from the OS |
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- ``grow`` |
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- ``attach`` |
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- ``detach`` |
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- ``setinfo`` |
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- ``verify`` |
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All scripts will be called with no arguments and get their input via |
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``EXTP_name`` |
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ExtStorage parameter, where `name` is the parameter in |
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upper-case (same as OS interface's ``OSP_*`` parameters). |
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``VOL_METADATA`` |
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A string containing metadata to be set for the volume. |
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This is exported only to the ``setinfo`` script. |
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All scripts except `attach` should return 0 on success and non-zero on |
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error, accompanied by an appropriate error message on stderr. The |
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To support the ExtStorage interface, we will introduce a new disk |
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template called `ext`. This template will implement the existing Ganeti |
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disk interface in `lib/bdev.py` (create, remove, attach, assemble, |
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shutdown, grow), and will simultaneously pass control to the external
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scripts to actually handle the above actions. The `ext` disk template
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will act as a translation layer between the current Ganeti disk |
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shutdown, grow, setinfo), and will simultaneously pass control to the
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external scripts to actually handle the above actions. The `ext` disk
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template will act as a translation layer between the current Ganeti disk
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interface and the ExtStorage providers. |
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We will also introduce a new IDISK_PARAM called `IDISK_PROVIDER = |
| b/man/ganeti-extstorage-interface.rst | ||
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REFERENCE |
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--------- |
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There are seven required files: *create*, *attach*, *detach*, *remove*, |
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*grow*, *verify* (executables) and *parameters.list* (text file). |
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There are eight required files: *create*, *attach*, *detach*, *remove*, |
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*grow*, *setinfo*, *verify* (executables) and *parameters.list* |
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(text file). |
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Common environment |
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~~~~~~~~~~~~~~~~~~ |
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variable, prefixed with ``EXTP_``, and upper-cased. For example, a |
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``fromsnap`` parameter will be exported as ``EXTP_FROMSNAP``. |
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VOL_METADATA |
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Available only to the **setinfo** script. A string containing |
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metadata to be associated with the volume. Currently, Ganeti sets |
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this value to ``originstname+X`` where ``X`` is the instance's name. |
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EXECUTABLE SCRIPTS |
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------------------ |
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The script returns ``0`` on success. |
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setinfo |
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~~~~~~~ |
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This script is used to add metadata to an existing volume. It is helpful |
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when we need to keep an external, Ganeti-independent mapping between |
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instances and volumes; primarily for recovery reasons. This is provider |
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specific and the author of the provider chooses whether/how to implement |
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this. You can just exit with ``0``, if you do not want to implement this |
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feature, without harming the overall functionality of the provider. |
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The ``VOL_METADATA`` variable contains the metadata of the volume. |
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Currently, Ganeti sets this value to ``originstname+X`` where ``X`` is |
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the instance's name. |
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The script returns ``0`` on success. |
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verify |
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~~~~~~ |
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Backwards compatibility |
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~~~~~~~~~~~~~~~~~~~~~~~ |
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The ExtStorage Interface was introduced in Ganeti 2.6.
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Ganeti 2.6 and up is compatible with the ExtStorage Interface.
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The ExtStorage Interface was introduced in Ganeti 2.7.
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Ganeti 2.7 and up is compatible with the ExtStorage Interface.
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Common behaviour |
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~~~~~~~~~~~~~~~~ |
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