Revision d3b06210 doc/design-partitioned.rst

b/doc/design-partitioned.rst
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Exclusive use of disks
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``exclusive_storage`` is a configuration flag at node-group and cluster


  		





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level. When it's enabled, Ganeti will allocate entire disks to


  		





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instances. Though it's possible to think of ways of doing something


  		





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similar for other storage back-ends, this design targets only ``plain``


  		





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and ``drbd``. The name is generic enough in case the feature will be


  		





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extended to other back-ends.


  		





  
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``exclusive_storage`` is a new node parameter. When it's enabled, Ganeti


  		





  
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will allocate entire disks to instances. Though it's possible to think


  		





  
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of ways of doing something similar for other storage back-ends, this


  		





  
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design targets only ``plain`` and ``drbd``. The name is generic enough


  		





  
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in case the feature will be extended to other back-ends. The flag value


  		





  
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should be homogeneous within a node-group; ``cluster-verify`` will report


  		





  
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any violation of this condition.


  		





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Ganeti will consider each physical volume in the destination volume


  		





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group as a host disk (for proper isolation, an administrator should


  		





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When creating a new disk for an instance, Ganeti will allocate the


  		





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minimum number of PVs to hold the disk, and those PVs will be excluded


  		





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from the pool of available PVs by marking them as unallocatable; in this


  		





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way, PVs won't be shared between instance disks, and any remaining space


  		





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won't be used by mistake for anything else. The underlying LV will be


  		





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striped, when striping is allowed by the current configuration. Ganeti


  		





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will continue to track only the LVs, and query the LVM layer to figure


  		





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out which PVs are available and how much space is free.


  		





  
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from the pool of available PVs for further disk creations. The


  		





  
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underlying LV will be striped, when striping is allowed by the current


  		





  
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configuration. Ganeti will continue to track only the LVs, and query the


  		





  
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LVM layer to figure out which PVs are available and how much space is


  		





  
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free. Yet, creation, disk growing, and free-space reporting will ignore


  		





  
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any partially allocated PVs, so that PVs won't be shared between


  		





  
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instance disks.


  		





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For compatibility with the DRBD template and to take into account disk


  		





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variability, Ganeti will always subtract 2% (this will be a parameter)


  		












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