[Bug 2165345] Re: [SRU] Allow 4k aligned IO for windows guests

[Seyeong Kim]

Hey @raineszm

Thank you for your patch.

Why don't we use original LP for SRU as well?
it's easier to trace from upstream.

And you need to do SRU for Ubuntu releases first like jammy noble etc..

Thanks.

https://ubuntu.com/project/docs/SRU/reference/requirements/#bugs

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https://bugs.launchpad.net/bugs/2165345

Title:
  [SRU] Allow 4k aligned IO for windows guests

Status in Ubuntu Cloud Archive:
  In Progress
Status in Ubuntu Cloud Archive antelope series:
  In Progress
Status in Ubuntu Cloud Archive bobcat series:
  In Progress
Status in Ubuntu Cloud Archive caracal series:
  In Progress
Status in Ubuntu Cloud Archive dalmatian series:
  In Progress
Status in Ubuntu Cloud Archive epoxy series:
  In Progress
Status in Ubuntu Cloud Archive flamingo series:
  In Progress
Status in Ubuntu Cloud Archive yoga series:
  In Progress
Status in Ubuntu Cloud Archive zed series:
  In Progress
Status in cinder package in Ubuntu:
  In Progress
Status in cinder source package in Jammy:
  In Progress
Status in cinder source package in Noble:
  In Progress

Bug description:
  [ Impact ]

  Ceph performs much better when I/O is 4k-aligned otherwise it has to
  read the 4k from disk, modify and write it again. Linux guests
  generally submit 4k-aligned I/O, however Windows guests generally
  submit 512b-aligned I/O. This can lead to significantly degraded
  performance for Openstack Windows guests when using the Ceph RBD
  backend.

  This SRU backports upstream patches[0-2] which enable hinting the
  logical block size of cinder devices to Nova and which in turn allows
  the Windows guest to perform 4k-aligned I/O.

  [ Test Plan ]

  1. Deploy openstack with cinder enabled and the ceph backend

  2. Create a new volume and ensure that the blocksize is not passed to
  libvirt

  3. Create a new volume with the disk_geometry option and ensure that
  the block size is properly passed to libvirt

  [ Where problems could occur ]

  * Virtual disks may not support setting block size [0]. As a result, setting the disk_geometry on LUN drives may cause errors in Nova. This is mitigated by leaving the disk_geometry option unset by default and allowing users to opt in on a driver by driver basis.
      * This has already been surfaced and addressed by the second patch of the series [2].

  [ Other Info ]

  * As noted in [0], for existing volumes, the libvirt xml will need to be regenerated for the effects to be seen e.g., by reattaching the volume. See the release-notes for the patch [1] for more details.
      * A corollary of the above, after some discussion with @mruffell, its probably best to backport this to interim releases as well as LTS, to minimize the number of times this detach/re-attach process needs to be carried out.

  [0]: https://bugs.launchpad.net/bugs/2127196
  [1]: https://review.opendev.org/c/openstack/cinder/+/658283
  [2]: https://review.opendev.org/c/openstack/cinder/+/975540

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