linux-kernel - Re: [PATCH v4 2/2] md: allow configuring logical_block

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Message-ID: <9041896d-e4f8-c231-e8ea-5d82f8d3b0d2@huaweicloud.com>
Date: Mon, 15 Sep 2025 10:15:41 +0800
From: Li Nan <linan666@...weicloud.com>
To: Xiao Ni <xni@...hat.com>, linan666@...weicloud.com
Cc: corbet@....net, song@...nel.org, yukuai3@...wei.com, hare@...e.de,
 martin.petersen@...cle.com, bvanassche@....org, filipe.c.maia@...il.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-raid@...r.kernel.org, yangerkun@...wei.com, yi.zhang@...wei.com
Subject: Re: [PATCH v4 2/2] md: allow configuring logical_block_size



在 2025/9/15 8:33, Xiao Ni 写道:
> Hi Nan
> 
> On Thu, Sep 11, 2025 at 3:41 PM <linan666@...weicloud.com> wrote:
>>
>> From: Li Nan <linan122@...wei.com>
>>
>> Previously, raid array used the maximum logical_block_size (LBS) of
>> all member disks. Adding a larger LBS during disk at runtime could
>> unexpectedly increase RAID's LBS, risking corruption of existing
>> partitions.
> 
> Could you describe more about the problem? It's better to give some
> test steps that can be used to reproduce this problem.

Thanks for your review. I will add reproducer in the next version.

>>
>> Simply restricting larger-LBS disks is inflexible. In some scenarios,
>> only disks with 512 LBS are available currently, but later, disks with
>> 4k LBS may be added to the array.
>>
>> Making LBS configurable is the best way to solve this scenario.
>> After this patch, the raid will:
>>    - stores LBS in disk metadata.
>>    - add a read-write sysfs 'mdX/logical_block_size'.
>>
>> Future mdadm should support setting LBS via metadata field during RAID
>> creation and the new sysfs. Though the kernel allows runtime LBS changes,
>> users should avoid modifying it after creating partitions or filesystems
>> to prevent compatibility issues.
> 
> Because it only allows setting when creating an array. Can this be
> done automatically in kernel space?
> 
> Best Regards
> Xiao

The kernel defaults LBS to the max among all rdevs. When creating RAID
with mdadm, if mdadm doesn't set LBS explicitly, how does the kernel
learn the intended value?

Gunaghao previously submitted a patch related to mdadm:
https://lore.kernel.org/all/3a9fa346-1041-400d-b954-2119c1ea001c@huawei.com/

-- 
Thanks,
Nan