[tahoe-lafs-trac-stream] [tahoe-lafs] #1293: servers-of-happiness is too conservative when K = 1

[tahoe-lafs]

#1293: servers-of-happiness is too conservative when K = 1
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     Reporter:           |      Owner:  davidsarah
  davidsarah             |     Status:  assigned
         Type:  defect   |  Milestone:  1.11.0
     Priority:  major    |    Version:  1.8.1
    Component:  code     |   Keywords:  servers-of-happiness usability
   Resolution:           |  availability
Launchpad Bug:           |
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Old description:

> When K = 1, any single share is sufficient to reconstruct the file.
> However, the servers-of-happiness code will still require that there are
> H servers with unique share numbers. It should not care about the share
> numbers.
>
> (We knew of examples with small K where the maximum matching definition
> of servers-of-happiness was conservative relative to the original
> definition, e.g. [ticket:778#comment:198]. However, for K > 1 it is more
> space-efficient to use the maximum matching definition. For K = 1 it is
> not.)

New description:

 When K = 1, any single share is sufficient to reconstruct the file.
 However, the servers-of-happiness code will still require that there are H
 servers with unique share numbers. It should not care about the share
 numbers.

 (We knew of examples with small K where the maximum matching definition of
 servers-of-happiness was conservative relative to the original definition,
 e.g. [ticket:778#comment:198]. However, for K > 1 it is more space-
 efficient to use the maximum matching definition. For K = 1 it is not.)

--

Comment (by markberger):

 For example, if we have a share distribution like this:

 * Server A: [1]
 * Server B: [1]
 * Server C: [1]

 with k = 1 and h = 3, the placement will be considered unhealthy even
 though we don't care about the share numbers because any single share is
 sufficient to reconstruct the file.

-- 
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1293#comment:4>
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