From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.de>
Subject: Re: What is the sector size in /sys/block/md*/md items?
Date: Mon, 24 Feb 2014 13:29:44 +1100
Message-ID: <20140224132944.435c9a2e@notabene.brown>
References: <5307F95E.70501@eyal.emu.id.au>
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To: Eyal Lebedinsky <eyal@eyal.emu.id.au>
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On Sat, 22 Feb 2014 12:11:58 +1100 Eyal Lebedinsky <eyal@eyal.emu.id.au>
wrote:

> I am reading the kernel Documentation/md.txt.
>=20
> It explains what md the items in sysfs mean. It refers a few times to "se=
ctors".
> - Are we talking 512 bytes or the underlying physical disk sector size?

Always 512 bytes.

> - Do all disks in an array need to have the same sector size?

No.

>=20
> Seeing how md can be built over physical disks, partitions, loop mounts a=
nd more,
> I expect that 'sector' is short for '512 bytes' and real disk sector size=
 is not
> relevant here.

Correct.

>=20
> Nevertheless, there is md*/queue/hw_sector_size which gives 512. So there=
 are now
> a few sector sizes (the array and the underlying devices) and the text do=
es not
> make it clear which is used where. I assume the array cluster size is the=
 one
> referred to in this document.

I was never happy when 'queue' appeared under md*.  It is almost entirely
irrelevant.

Feel free to post a patch to clarify md.txt.

Thanks,
NeilBrown


>=20
> TIA
>=20
> --
> Eyal Lebedinsky (eyal@eyal.emu.id.au)
> --
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