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[Andrew Bogott <1513654@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

I use qcow images and have disk_allocation_ratio == 2.1 to allow large
amounts of overcommitting of disk space.  To quote the nova config
reference:

>  If the value is set to >1, we recommend keeping track of the free disk space, as the value approaching 0 may result in the incorrect 
>     functioning of instances using it at the moment.

Good advice, but 'keeping track' can be a bit impractical at times.  I
just now had the scheduler drop a large sized instance onto a server
with a 98% full drive since the behavior of disk_allocation_ratio
intentionally ignores the actual free space on the drive.

I propose that we add an additional config setting to the disk scheduler
so that I can overschedule but can /also/ request that the scheduler
stop piling things onto an already groaning server.

** Affects: nova
     Importance: Undecided
         Status: In Progress

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https://bugs.launchpad.net/bugs/1513654

Title:
  scheduler:  disk_filter permits scheduling on full drives

Status in OpenStack Compute (nova):
  In Progress

Bug description:
  I use qcow images and have disk_allocation_ratio == 2.1 to allow large
  amounts of overcommitting of disk space.  To quote the nova config
  reference:

  >  If the value is set to >1, we recommend keeping track of the free disk space, as the value approaching 0 may result in the incorrect 
  >     functioning of instances using it at the moment.

  Good advice, but 'keeping track' can be a bit impractical at times.  I
  just now had the scheduler drop a large sized instance onto a server
  with a 98% full drive since the behavior of disk_allocation_ratio
  intentionally ignores the actual free space on the drive.

  I propose that we add an additional config setting to the disk
  scheduler so that I can overschedule but can /also/ request that the
  scheduler stop piling things onto an already groaning server.

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