yahoo-eng-team team mailing list archive

[Gorka Eguileor <2023210@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Assuming we have configured everything correctly in OpenStack to use
discard on Cinder block devices and we  have checked that discard works,
the wrong values for discard_granularity` and `discard_max_bytes` are
reported to the VM's guest Operating System.

We can confirm this by checking the values on the host and the guest and
see that they don't match:

- `/sys/block/<dev>/queue/discard_max_bytes`
- `/sys/block/<dev>/queue/discard_granularity`.

The problem is that there is no code in Nova to set these values in
libvirt, nor does Cinder or os-brick have any code to detect the right
values to set.

The libvirt fuctionality to set `discard_granularity` and
`max_unmap_size` already exists:
(https://bugzilla.redhat.com/show_bug.cgi?id=1408553.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2023210

Title:
  Wrong discard_granurality and discard_max_bytes reported in guest OS

Status in OpenStack Compute (nova):
  New

Bug description:
  Assuming we have configured everything correctly in OpenStack to use
  discard on Cinder block devices and we  have checked that discard
  works, the wrong values for discard_granularity` and
  `discard_max_bytes` are reported to the VM's guest Operating System.

  We can confirm this by checking the values on the host and the guest
  and see that they don't match:

  - `/sys/block/<dev>/queue/discard_max_bytes`
  - `/sys/block/<dev>/queue/discard_granularity`.

  The problem is that there is no code in Nova to set these values in
  libvirt, nor does Cinder or os-brick have any code to detect the right
  values to set.

  The libvirt fuctionality to set `discard_granularity` and
  `max_unmap_size` already exists:
  (https://bugzilla.redhat.com/show_bug.cgi?id=1408553.

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