min_size vs. K in erasure coded pools

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Hi!

While trying to understand erasure coded pools, I would have expected that "min_size" of a pool is equal to the "K" parameter. But it turns out, that it is always K+1.

Isn't the description of erasure coding misleading then? In a K+M setup, I would expect to be good (in the sense of "no service impact"), even if M OSDs are lost. But in reality, my clients would already experience an impact when M-1 OSDs are lost. This means, you should always consider one more spare than you would do in e.g. a classic RAID setup, right?

Joern

--
Jörn Clausen
Daten- und Rechenzentrum
GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
Düsternbrookerweg 20
24105 Kiel

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