Re: RAID56 Warning on "multiple serious data-loss bugs"

From: DanglingPointer <danglingpointerexception@gmail.com>
To: linux-btrfs <linux-btrfs@vger.kernel.org>
Cc: kreijack@inwind.it, Chris Murphy <lists@colorremedies.com>,
	Remi Gauvin <remi@georgianit.com>
Subject: Re: RAID56 Warning on "multiple serious data-loss bugs"
Date: Wed, 30 Jan 2019 12:41:27 +1100	[thread overview]
Message-ID: <d3de555c-3e44-533d-5ae2-88a5abaf0401@gmail.com> (raw)
In-Reply-To: <80f46e68-4cda-3a22-385b-0ab0a47b079a@libero.it>

Going back to my original email, would the BTRFS wiki admins consider a 
better more reflective update of the RAID56 status page?

It still states "multiple serious data-loss bugs" which as Qu Wenruo has 
already clarified is not the case.  The only "bug" left is the write 
hole edge-case problem.

On 30/1/19 6:47 am, Goffredo Baroncelli wrote:
> On 29/01/2019 20.02, Chris Murphy wrote:
>> On Mon, Jan 28, 2019 at 3:52 PM Remi Gauvin <remi@georgianit.com> wrote:
>>> On 2019-01-28 5:07 p.m., DanglingPointer wrote:
>>>
>>>>  From Qu's statement and perspective, there's no difference to other
>>>> non-BTRFS software RAID56's out there that are marked as stable (except
>>>> ZFS).
>>>> Also there are no "multiple serious data-loss bugs".
>>>> Please do consider my proposal as it will decrease the amount of
>>>> incorrect paranoia that exists in the community.
>>>> As long as the Wiki properly mentions the current state with the options
>>>> for mitigation; like backup power and perhaps RAID1 for metadata or
>>>> anything else you believe as appropriate.
>>> Should implement some way to automatically scrub on unclean shutdown.
>>> BTRFS is the only (to my knowlege) Raid implementation that will not
>>> automatically detect an unclean shutdown and fix the affected parity
>>> blocks, (either by some form of write journal/write intent map, or full
>>> resync.)
>> There's no dirty bit set on mount, and thus no dirty bit to unset on
>> clean mount, from which to infer a dirty unmount if it's present at
>> the next mount.
> It would be sufficient to use the log, which BTRFS already has. During each transaction, when an area is touched by a rwm cycle, it has to tracked in the log.
> In case of unclean shutdown, it is already implemented a way to replay the log. So it would be sufficient to track a scrub of these area as "log replay".
>
> Of course I am talking as not a BTRFS developers, so the reality could be more complex: e.g. I don't know how it would be easy to raise a scrub process on per area basis.
>
> BR
> G.Baroncelli
>
>
>