From: tudor@tudorholton.com
To: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] (Why) Does lvmcreate --raid6 need 5 drives?
Date: Tue, 18 Sep 2018 09:41:25 +1000 [thread overview]
Message-ID: <086f04e0e43d27d5637a7516c4a27877@tudorholton.com> (raw)
In-Reply-To: <a032c5fd-5381-49f3-0b16-a9baac9b5e43@redhat.com>
--------snip------
> 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.
next prev parent reply other threads:[~2018-09-17 23:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-16 23:36 [linux-lvm] (Why) Does lvmcreate --raid6 need 5 drives? tudor
2018-09-17 12:41 ` Heinz Mauelshagen
2018-09-17 23:41 ` tudor [this message]
2018-09-18 9:14 ` Heinz Mauelshagen
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