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From: Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>
To: "Kengo.M" <kengo@kyoto-arc.or.jp>
Cc: linux-raid@vger.kernel.org
Subject: Re: Number of parity disks
Date: Sat, 5 Mar 2022 09:56:31 +0100	[thread overview]
Message-ID: <YiMlvzrUwFJtxqfr@lazy.lzy> (raw)
In-Reply-To: <p06001087de48ad4092ee@kyoto-arc.or.jp>

On Sat, Mar 05, 2022 at 03:09:55PM +0900, Kengo.M wrote:
> Hi Folks
> 
> I use mdadm conveniently.
> 
> Let me ask a very very basic question.
> 
> One parity disk can be used in RAID 5 and 2 parity disks can be used in RAID 6.
> ZFS RAIDZ-3 (raidz3) can use 3 parity disks.
> 
> Is it difficult to increase the number of parity disks to 4, 5 or more.
> If so, is the reason for this because of the time it takes to generate the
> parity bits?

There was a project, some times ago, with
the aim to create a library, initially for
btrfs, capable of adding "n" parities.

This should have been usable by md as well.

The problem is that the Vandermonde matrix
might not invertible with more than 2 parities.
So, they've to use a Cauchy matrix.

It might be that performances are degrading
quite a lot.

I'm not sure about the status of such library,
maybe you can ask in the btrfs mailing list.

On the other hand, 3 parities (or more) case
might be a bit an overkill.
For md could be better to have things like
RAID-61 or similar.

bye,

-- 

piergiorgio

  reply	other threads:[~2022-03-05  9:05 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-04 17:55 [PATCH 1/2] nvme: remove support or stream based temperature hint Christoph Hellwig
2022-03-04 17:55 ` [PATCH 2/2] block: remove the per-bio/request write hint Christoph Hellwig
2022-03-04 19:24   ` Jens Axboe
2022-03-04 22:12   ` Dave Chinner
2022-03-05  5:19     ` Christoph Hellwig
2022-03-05  6:09       ` Number of parity disks Kengo.M
2022-03-05  8:56         ` Piergiorgio Sartor [this message]
2022-03-05 21:40       ` [PATCH 2/2] block: remove the per-bio/request write hint Dave Chinner
2022-03-05 23:55         ` Bart Van Assche
2022-03-06 17:11         ` Jens Axboe
2022-03-06 18:01           ` Christoph Hellwig
2022-03-06 18:06             ` Jens Axboe
2022-03-06 23:17               ` Dave Chinner
     [not found]                 ` <CGME20220309042324epcas1p111312e20f4429dc3a17172458284a923@epcas1p1.samsung.com>
2022-03-09 13:31                   ` Manjong Lee
2022-03-09  8:24                     ` Paul Menzel
2022-03-10 11:34                     ` [EXT] " Luca Porzio (lporzio)
2022-03-10 12:15                       ` Jens Axboe
2022-03-10 18:50                         ` Luca Porzio (lporzio)
2022-03-10 19:10                           ` Jens Axboe
2022-03-10 19:34                             ` Bart Van Assche
2022-03-10 21:52                               ` Bean Huo (beanhuo)
2022-03-10 22:10                                 ` Jens Axboe
2022-03-11 16:45                                   ` Bart Van Assche
2022-03-11 16:56                                     ` Jens Axboe
2022-03-14  7:40                                       ` Avi Shchislowski
2022-03-14  8:00                                         ` hch
2022-03-14 19:50                                         ` Eric Biggers
2022-03-14 19:58                                         ` [EXT] " Jens Axboe
2022-03-15 15:36                                           ` Luca Porzio (lporzio)
2022-03-15 15:44                                             ` Jens Axboe
2022-03-10 22:18                                 ` Bart Van Assche
2022-03-11  5:31                                   ` Eric Biggers
2022-03-11  5:31                                     ` [f2fs-dev] " Eric Biggers
2022-03-11  9:21                                   ` Luca Porzio (lporzio)
2022-03-10 14:21                       ` hch
2022-03-10 18:51                         ` Luca Porzio (lporzio)
2022-03-10 19:14                           ` hch
2022-03-11  5:06                           ` Eric Biggers
2022-03-11  9:23                             ` Luca Porzio (lporzio)
2022-03-04 19:34 ` [PATCH 1/2] nvme: remove support or stream based temperature hint Keith Busch
2022-03-04 19:36   ` Christoph Hellwig
2022-03-04 19:38     ` Jens Axboe
2022-03-04 20:20 ` Jens Axboe
2023-01-03 23:40 Number of parity disks Kengo.M
2023-01-04 10:23 ` Hugo Mills

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