linux-kernel - Re: [PATCH v2 2/3] md: allow configuring logical_block

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Message-ID: <yq1zfcleyqv.fsf@ca-mkp.ca.oracle.com>
Date: Thu, 31 Jul 2025 01:36:15 -0400
From: "Martin K. Petersen" <martin.petersen@...cle.com>
To: linan666@...weicloud.com
Cc: <song@...nel.org>, <yukuai3@...wei.com>, <martin.petersen@...cle.com>,
        <hare@...e.de>, <axboe@...nel.dk>, <linux-raid@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bvanassche@....org>,
        <hch@...radead.org>, <filipe.c.maia@...il.com>, <yangerkun@...wei.com>,
        <yi.zhang@...wei.com>
Subject: Re: [PATCH v2 2/3] md: allow configuring logical_block_size

> 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.

Having to have the foresight to preemptively configure a larger logical
block size at creation time also seems somewhat inflexible :)

In general I am not a big fan of mixing devices with different
properties. I have regretted stacking the logical block size on several
occasions.

I am also concerned about PI breaking if the logical block size facing
upwards does not match the actual logical block size of the component
devices below. In theory it should work with the PI interval exponent
but it is something that needs to be tested.

What if the MD device's configured logical block size is larger than the
physical block size of the underlying devices? Then we'll end up
reporting a logical block size larger than the physical block size. Ugh.

Oh, and what about atomics?

-- 
Martin K. Petersen