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From:   Phillip Susi <phill@thesusis.net>
To:     David T-G <davidtg-robot@justpickone.org>
Cc:     list Linux RAID <linux-raid@vger.kernel.org>
Subject: Re: raid10 redundancy
Date:   Thu, 13 May 2021 11:46:42 -0400
In-reply-to: <20210512172242.GX1415@justpickone.org>
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David T-G writes:

> RAID10 is striping AND mirroring (leaving out for the moment the distinction
> of striping mirrors vs mirroring stripes).  How can one have both with only
> two disks??  You either stripe the two disks together for more storage or
> mirror them for redundant storage, but I just don't see how one could do both.

In the default near layout, you don't get the striping with only two
disks; it is identical to raid1.  With the offset and far layouts
though, you do get the striping and the mirroring by mirroring each
stripe elsewhere on the disk ( one stripe down in the case of offset,
and in the second half of the disk in the case of far ).

With 3 disks, even the near layout benefits from striping.