From: Goffredo Baroncelli <kreijack@inwind.it>
To: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Cc: Christoph Anton Mitterer <calestyo@scientia.net>,
linux-btrfs@vger.kernel.org
Subject: Re: Status of RAID5/6
Date: Sat, 31 Mar 2018 10:16:26 +0200 [thread overview]
Message-ID: <b3214c3e-cf0c-4070-acbb-892a449476f8@inwind.it> (raw)
In-Reply-To: <20180331074320.GF2446@hungrycats.org>
On 03/31/2018 09:43 AM, Zygo Blaxell wrote:
>> The key is that if a data write is interrupted, all the transaction
>> is interrupted and aborted. And due to the COW nature of btrfs, the
>> "old state" is restored at the next reboot.
> This is not presently true with raid56 and btrfs. RAID56 on btrfs uses
> RMW operations which are not COW and don't provide any data integrity
> guarantee. Old data (i.e. data from very old transactions that are not
> part of the currently written transaction) can be destroyed by this.
Could you elaborate a bit ?
Generally speaking, updating a part of a stripe require a RMW cycle, because
- you need to read all data stripe (with parity in case of a problem)
- then you should write
- the new data
- the new parity (calculated on the basis of the first read, and the new data)
However the "old" data should be untouched; or you are saying that the "old" data is rewritten with the same data ?
BR
G.Baroncelli
--
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
next prev parent reply other threads:[~2018-03-31 8:16 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-21 16:50 Status of RAID5/6 Menion
2018-03-21 17:24 ` Liu Bo
2018-03-21 20:02 ` Christoph Anton Mitterer
2018-03-22 12:01 ` Austin S. Hemmelgarn
2018-03-29 21:50 ` Zygo Blaxell
2018-03-30 7:21 ` Menion
2018-03-31 4:53 ` Zygo Blaxell
2018-03-30 16:14 ` Goffredo Baroncelli
2018-03-31 5:03 ` Zygo Blaxell
2018-03-31 6:57 ` Goffredo Baroncelli
2018-03-31 7:43 ` Zygo Blaxell
2018-03-31 8:16 ` Goffredo Baroncelli [this message]
[not found] ` <28a574db-0f74-b12c-ab5f-400205fd80c8@gmail.com>
2018-03-31 14:40 ` Zygo Blaxell
2018-03-31 22:34 ` Chris Murphy
2018-04-01 3:45 ` Zygo Blaxell
2018-04-01 20:51 ` Chris Murphy
2018-04-01 21:11 ` Chris Murphy
2018-04-02 5:45 ` Zygo Blaxell
2018-04-02 15:18 ` Goffredo Baroncelli
2018-04-02 15:49 ` Austin S. Hemmelgarn
2018-04-02 22:23 ` Zygo Blaxell
2018-04-03 0:31 ` Zygo Blaxell
2018-04-03 17:03 ` Goffredo Baroncelli
2018-04-03 22:57 ` Zygo Blaxell
2018-04-04 5:15 ` Goffredo Baroncelli
2018-04-04 6:01 ` Zygo Blaxell
2018-04-04 21:31 ` Goffredo Baroncelli
2018-04-04 22:38 ` Zygo Blaxell
2018-04-04 3:08 ` Chris Murphy
2018-04-04 6:20 ` Zygo Blaxell
2018-03-21 20:27 ` Menion
2018-03-22 21:13 ` waxhead
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