Re: (Why) Does lvmcreate --raid6 need 5 drives?

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We do have a constraint in lvm2 to require the raid6 minimum for N to be 3.

Configuring a raid6 LV (an array by MD terms) with 2 data stripes is
suboptimal for performance,
because data striping is minimal in this case.  In addition, the
metadata overhead is maximal
for parity, P- and Q-syndromes being half of the brutto size of the raid6 LV.

My apologies. I googled "brutto size" but came up with nothing. I do have a basic understanding of P and Q syndromes so I think I have a vague understanding of your meaning.

I understand it's suboptimal, but not non-existent. In particular why is this a restriction and not just a warning?

Performance aside, I could also argue that there's a use case for a minimal (and not degraded) set before expansion.

Cheers,
Tudor.

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