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

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Message-ID: <95915b76-97ce-55b1-6a5a-7ff8a89bc430@huaweicloud.com>
Date: Thu, 24 Oct 2024 17:12:31 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: John Garry <john.g.garry@...cle.com>, 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

Hi,

在 2024/10/24 16:57, John Garry 写道:
> 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.

I mean the rdev flag, all underlying disks should set FailFast, so that
no BB will be present. rdev will just become faulty for the case IO
error.

r1/r10 bio failfast flags is for internal usage to handle IO error.

Thanks,
Kuai

> 
> Thanks,
> John
> 
> 
> .
>