linux-kernel - Re: [PATCH RFC 5/6] md/raid1: Handle bio

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Message-ID: <3654e52e-d51e-4a61-aead-789e745599bf@oracle.com>
Date: Thu, 24 Oct 2024 09:57:27 +0100
From: John Garry <john.g.garry@...cle.com>
To: Yu Kuai <yukuai1@...weicloud.com>, Geoff Back <geoff@...onlair.co.uk>,
        axboe@...nel.dk, hch@....de
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-raid@...r.kernel.org, martin.petersen@...cle.com,
        "yangerkun@...wei.com" <yangerkun@...wei.com>,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC 5/6] md/raid1: Handle bio_split() errors

On 24/10/2024 03:10, Yu Kuai wrote:
>> On 23/10/2024 12:46, Geoff Back wrote:
>>>>> Yes, raid1/raid10 write are the same. If you want to enable atomic 
>>>>> write
>>>>> for raid1/raid10, you must add a new branch to handle badblocks now,
>>>>> otherwise, as long as one copy contain any badblocks, atomic write 
>>>>> will
>>>>> fail while theoretically I think it can work.
>>>> Can you please expand on what you mean by this last sentence, "I think
>>>> it can work".
> 
> I mean in this case, for the write IO, there is no need to split this IO
> for the underlying disks that doesn't have BB, hence atomic write can
> still work. Currently solution is to split the IO to the range that all
> underlying disks doesn't have BB.

ok, right.

> 
>>>>
>>>> Indeed, IMO, chance of encountering a device with BBs and supporting
>>>> atomic writes is low, so no need to try to make it work (if it were
>>>> possible) - I think that we just report EIO.
> 
> If you want this, then make sure raid will set fail fast together with
> atomic write. This way disk will just faulty with IO error instead of
> marking with BB, hence make sure there are no BBs.

To be clear, you mean to set the r1/r10 bio failfast flag, right? There 
are rdev and also r1/r10 bio failfast flags.

Thanks,
John