DOCS: Optional filesystem for cinder image conversion

[Elena Taivan]

The information in this launchpad is for the following LP: https://bugs.launchpad.net/starlingx/+bug/1819688

Brief Description
-----------------

This feature provides an optional filesystem that can be used by cinder for qcow2 image conversion to raw.
By default, qcow2 image conversion is done by using the docker_lv filesystem.
To avoid the scenario of filling up the docker_lv filesystem, a new filesystem should be dedicated for image conversion.

Add a new filesystem for image conversion
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    New host_fs CLI command was provided for adding 'image-conversion' filesystem
    dedicated only for qcow2 image conversion:
        o system host-fs-add <hostname or id> <fs name=size>
    When 'image-conversion' filesystem is added, a new partition
    '/opt/conversion' is created and mounted.

    Notes
    =====
        1. The size of the 'image-conversion' should be big enough to accommodate
           any image that is uploaded to glance.
        2. Conversion filesystem can be added before/after stx-openstack is
           applied.
        3. If filesystem is not added on both controllers, stx-openstack will not
           use the new filesystem.
        4. If conversion filesystem is added after stx-openstack
           is applied, changes to stx-openstack will only take effect
           once the application is re-applied

    'Image-conversion' filesystem can be added only on controller nodes.

    Alarms for image-conversion will be raised:
    ===========================================
        o if image-conversion is not added on both controllers
        o if the size of the filesystem is not the same on both controllers

Remove the filesystem
~~~~~~~~~~~~~~~~~~~~~
    New host_fs CLI command was provided for removing 'image-conversion'
    filesystem
        o system host-fs-delete <hostname or id> <fs name>
    When 'image-conversion' is removed, '/opt/conversion' partition is also
    removed.

    Notes
    =====
        1. It is not allowed to delete image-conversion filesystem
           when stx-openstack is in applying/applied/removing state

It is not allowed to add/remove any other filesystem.

Resize the filesystem
~~~~~~~~~~~~~~~~~~~~~~
    The size of 'image-conversion' filesystem can be changed at runtime by using
    the existing CLI command
        o system host-fs-modify

[Bruce Jones (brucej)]

Question - does the system host-fs-add need to be run on both controllers separately?

[Elena Taivan (etaivan)]

not separately.
on the main controller, you can run system host-fs-add for controller-1, such as:
system host-fs-add controller-1 image-conversion=x

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/730529

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/731257

[OpenStack Infra (hudson-openstack)]

Change abandoned by Mary Camp (<email address hidden>) on branch: master
Review: https://review.opendev.org/731257
Reason: Submitted same change twice - abandon this one.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/730529
Committed: https://git.openstack.org/cgit/starlingx/docs/commit/?id=985212c0abcefd82972d003b064b028874ee0497
Submitter: Zuul
Branch: master

commit 985212c0abcefd82972d003b064b028874ee0497
Author: MCamp859 <email address hidden>
Date: Sun May 24 16:58:49 2020 -0400

    Add Cinder config guide for image conversion file system

    Guide describes how to create, modify, and delete optional
    file system used for image conversion.

    Closes-Bug: 1879632

    Change-Id: I59be43dbf3aed814273824df99125bedbb9bafbf
    Signed-off-by: MCamp859 <email address hidden>