Revision 5b53ca79 man/hail.rst

b/man/hail.rst
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DESCRIPTION
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-----------
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hail is a Ganeti IAllocator plugin that allows automatic instance
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placement and automatic instance secondary node replacement using the
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same algorithm as **hbal**(1).
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hail is a Ganeti IAllocator plugin that implements the instance
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placement and movement using the same algorithm as **hbal**(1).
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The program takes input via a JSON-file containing current cluster
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state and the request details, and output (on stdout) a JSON-formatted
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The program uses a simplified version of the hbal algorithm.
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For relocations, we try to change the secondary node of the instance
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to all the valid other nodes; the node which results in the best
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cluster score is chosen.
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For single-node allocations (non-mirrored instances), again we
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select the node which, when chosen as the primary node, gives the best
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score.
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pair; this is the only choice where the algorithm is non-trivial
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with regard to cluster size.
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For node evacuations (*multi-evacuate* mode), we iterate over all
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instances which live as secondaries on those nodes and try to relocate
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them using the single-instance relocation algorithm.
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For node changes (*change-node* mode), we currently support DRBD
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instances only, and all three modes (primary changes, secondary changes
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and all node changes).
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For group moves (*change-group* mode), again only DRBD is supported, and
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we compute the correct sequence that will result in a group change; job
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failure mid-way will result in a split instance. The choice of node(s)
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on the target group is based on the group score, and the choice of group
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is based on the same algorithm as allocations (group with lowest score
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after placement).
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The deprecated *relocate* and *multi-evacuate* modes are no longer
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supported.
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In all cases, the cluster scoring is identical to the hbal algorithm.
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In all cases, the cluster (or group) scoring is identical to the hbal
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algorithm.
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OPTIONS
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