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[Brooks Kaminski <bhkaminski@xxxxxxxxx>]

Public bug reported:

Currently the code creates a mis-aligned partition on the ephemeral
drive during disk creation.  This is done by the code attempting to
create the partition at the 0 sector which then defaults to 1.  When
attempting to replicate this setup by hand using parted (as the code
does) it will alert you of the misalignment such as:

test@testbox:~# parted --script /dev/xvde -- mkpart primary 0 -0
Warning: The resulting partition is not properly aligned for best performance.

This results in the possibility of significantly slower read speeds
against the disk, and some impact against the write speeds.  The
relevant code responsible for the ephemeral partition size configuration
can be found at:

https://github.com/openstack/nova/blob/master/nova/virt/xenapi/vm_utils.py#L1043-L1057

And the actual parted command utilizing this can be found here:

https://github.com/openstack/nova/blob/master/nova/virt/xenapi/vm_utils.py#L992-L1006

I have already committed a simple change for this awaiting review --
Change ID: I2b33659d66ce5ba8a361386277c5fee47ddcde94

https://review.openstack.org/#/c/203323/

Testing for this bug can be accomplished by creating a VM with an
ephemeral drive and monitoring r/w speeds with the default partitioning
and then with custom partitioning (2048 start sector) using dd/hdparm,
etc.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1487300

Title:
  Misaligned partitions for ephemeral drives (Xenapi)

Status in OpenStack Compute (nova):
  New

Bug description:
  Currently the code creates a mis-aligned partition on the ephemeral
  drive during disk creation.  This is done by the code attempting to
  create the partition at the 0 sector which then defaults to 1.  When
  attempting to replicate this setup by hand using parted (as the code
  does) it will alert you of the misalignment such as:

  test@testbox:~# parted --script /dev/xvde -- mkpart primary 0 -0
  Warning: The resulting partition is not properly aligned for best performance.

  This results in the possibility of significantly slower read speeds
  against the disk, and some impact against the write speeds.  The
  relevant code responsible for the ephemeral partition size
  configuration can be found at:

  https://github.com/openstack/nova/blob/master/nova/virt/xenapi/vm_utils.py#L1043-L1057

  And the actual parted command utilizing this can be found here:

  https://github.com/openstack/nova/blob/master/nova/virt/xenapi/vm_utils.py#L992-L1006

  I have already committed a simple change for this awaiting review --
  Change ID: I2b33659d66ce5ba8a361386277c5fee47ddcde94

  https://review.openstack.org/#/c/203323/

  Testing for this bug can be accomplished by creating a VM with an
  ephemeral drive and monitoring r/w speeds with the default
  partitioning and then with custom partitioning (2048 start sector)
  using dd/hdparm, etc.

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