58 lines
3.1 KiB
YAML
58 lines
3.1 KiB
YAML
---
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features:
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A new configuration option, ``[compute]/max_disk_devices_to_attach``, which
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defaults to ``-1`` (unlimited), has been added and can be used to configure
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the maximum number of disk devices allowed to attach to a single server,
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per compute host. Note that the number of disks supported by a server
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depends on the bus used. For example, the ``ide`` disk bus is limited to 4
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attached devices.
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Usually, disk bus is determined automatically from the device type or disk
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device, and the virtualization type. However, disk bus
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can also be specified via a block device mapping or an image property.
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See the ``disk_bus`` field in
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https://docs.openstack.org/nova/latest/user/block-device-mapping.html
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for more information about specifying disk bus in a block device mapping,
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and see
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https://docs.openstack.org/glance/latest/admin/useful-image-properties.html
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for more information about the ``hw_disk_bus`` image property.
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The configured maximum is enforced during server create, rebuild, evacuate,
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unshelve, live migrate, and attach volume. When the maximum is exceeded
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during server create, rebuild, evacuate, unshelve, or live migrate, the
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server will go into ``ERROR`` state and the server fault message will
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indicate the failure reason. When the maximum is exceeded during a server
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attach volume API operation, the request will fail with a
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``403 HTTPForbidden`` error.
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issues:
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Operators changing the ``[compute]/max_disk_devices_to_attach`` on a
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compute service that is hosting servers should be aware that it could
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cause rebuilds to fail, if the maximum is decreased lower than the number
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of devices already attached to servers. For example, if server A has 26
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devices attached and an operators changes
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``[compute]/max_disk_devices_to_attach`` to 20, a request to rebuild server
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A will fail and go into ERROR state because 26 devices are already
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attached and exceed the new configured maximum of 20.
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Operators setting ``[compute]/max_disk_devices_to_attach`` should also be
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aware that during a cold migration, the configured maximum is only enforced
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in-place and the destination is not checked before the move. This means if
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an operator has set a maximum of 26 on compute host A and a maximum of 20
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on compute host B, a cold migration of a server with 26 attached devices
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from compute host A to compute host B will succeed. Then, once the server
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is on compute host B, a subsequent request to rebuild the server will fail
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and go into ERROR state because 26 devices are already attached and exceed
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the configured maximum of 20 on compute host B.
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The configured maximum is not enforced on shelved offloaded servers, as
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they have no compute host.
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upgrade:
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The new configuration option, ``[compute]/max_disk_devices_to_attach``
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defaults to ``-1`` (unlimited). Users of the libvirt driver should be
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advised that the default limit for non-ide disk buses has changed from 26
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to unlimited, upon upgrade to Stein. The ``ide`` disk bus continues to be
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limited to 4 attached devices per server.
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