linux-kernel - Re: RAID4 with no striping mode request

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Message-ID: <CAPhsuW4XPqY18k4DB2YXqaNgABp3HYYQtS7u0bGfjBcTgkpXkQ@mail.gmail.com>
Date:   Tue, 14 Feb 2023 10:37:58 -0800
From:   Song Liu <song@...nel.org>
To:     Kyle Sanderson <kyle.leet@...il.com>
Cc:     John Stoffel <john@...ffel.org>,
        device-mapper development <dm-devel@...hat.com>,
        linux-raid@...r.kernel.org,
        Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: RAID4 with no striping mode request

Hi Kyle,

On Mon, Feb 13, 2023 at 1:12 PM Kyle Sanderson <kyle.leet@...il.com> wrote:
>
[...]

> >
> > > The benefit of this can be the data disks are all zoned, and you can
> > > have a fast parity disk and still maintain excellent performance in
> > > the array (limited only by the speed of the disk in question +
> > > parity). Additionally, should 2 disks fail, you've either lost the
> > > parity and data disk, or 2 data disks with the parity and other disks
> > > not lost.

I think I understand the high level idea here. But I think we need a lot more
details on how to implement this, and what the system would look like.
Also, I don't quite follow why the data disks can be zoned devices and
still maintain excellent performance.

> > > I was reading through the DM and MD code and it looks like everything
> > > may already be there to do this, just needs (significant) stubs to be
> > > added to support this mode (or new code). Snapraid is a friendly (and
> > > respectable) implementation of this. Unraid and Synology SHR compete
> > > in this space, as well as other NAS and enterprise SAN providers.

Assume we figure out all the details. I will be happy to review patches in
MD code. But I won't be able to develop this feature myself.

Thanks,
Song