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Message-ID: <e7b9a1ae-3dd9-84a1-561f-88d1cf3bf117@huaweicloud.com>
Date:   Mon, 29 May 2023 21:14:43 +0800
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Subject: Re: [PATCH] md/raid10: prioritize adding disk to 'removed' mirror
To:     Yu Kuai <yukuai1@huaweicloud.com>, linan666@huaweicloud.com,
        song@kernel.org
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, houtao1@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230527092007.3008856-1-linan666@huaweicloud.com>
 <45ee7cb9-6651-46a5-87a2-dd66532084d7@huaweicloud.com>
From:   Li Nan <linan666@huaweicloud.com>
In-Reply-To: <45ee7cb9-6651-46a5-87a2-dd66532084d7@huaweicloud.com>
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在 2023/5/29 21:00, Yu Kuai 写道:
> Hi,
> 
> 在 2023/05/27 17:20, linan666@huaweicloud.com 写道:
>> From: Li Nan <linan122@huawei.com>
>>
>> When add a new disk to raid10, it will traverse conf->mirror from start
>> and find one of the following mirror to add:
>>    1. mirror->rdev is set to WantReplacement and it have no replacement,
>>       set new disk to mirror->replacement.
>>    2. no mirror->rdev, set new disk to mirror->rdev.
>>
>> There is a array as below (sda is set to WantReplacement):
>>
>>      Number   Major   Minor   RaidDevice State
>>         0       8        0        0      active sync set-A   /dev/sda
>>         -       0        0        1      removed
>>         2       8       32        2      active sync set-A   /dev/sdc
>>         3       8       48        3      active sync set-B   /dev/sdd
>>
>> Use 'mdadm --add' to add a new disk to this array, the new disk will
>> become sda's replacement instead of add to removed position, which is
>> confusing for users. Meanwhile, after new disk recovery success, sda
>> will be set to Faulty.
>>
>> Prioritize adding disk to 'removed' mirror is a better choice. In the
>> above scenario, the behavior is the same as before, except sda will not
>> be deleted. Before other disks are added, continued use sda is more
>> reliable.
>>
> 
> I think this change make sense, however, it's better to do this for all
> personality instead of just for raid10.
> 
> Thanks,
> Kuai

raid5 is currently like this. If others are OK with this changes to 
raid10, I will modify raid1 later.

-- 
Thanks,
Nan