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Date:	Mon, 22 Apr 2013 08:35:49 +1000
From:	NeilBrown <>
To:	Vasiliy Tolstov <>
Subject: Re: mdadm raid1 regression

On Thu, 18 Apr 2013 14:38:53 +0400 Vasiliy Tolstov <>

> Hello. I'm using linux 3.8.6 and mdadm 3.2.6 (from git).
> I have many raid1 arrays that have data offset 2048 (metadata 1.2,
> created with various mdadm versions but mostly 3.2.1 on linux 2.6.32).
> If i create raid1 with never mdadm on 3.8.6 i have data offset 8192?? Why?

More room for various useful things.
In particular, if you one day want to convert this raid1 to a raid5, then
having a bit of extra space at the front will mean you can avoid a 'backup
file' and all the problems they cause (code for this isn't quite ready, but
is getting there).

> My problem:
> Sometimes i'm doing mdadm --zero-superblock on both parts of array and
> re-create it. On older systems i have no errors. On new (linux 3.8.6
> and mdadm 3.2.6) i get corrupted ext3 fs and partition table. Why this
> happening?

Why are you doing that?

> P.S. If i use mdadm 3.2.2 i get data offset 4096 that not breaks data,
> but inconsistent with older versions.

I suggest you use mdadm 3.2.2 then.

> P.P.S. I'm try to specify --data-offset when create array but as i see
> - its ignored and data offset still have 8192).

I'll try to make sure that works correctly for the next release.
Thanks for the report.


> Thanks!
> --
> Vasiliy Tolstov,
> e-mail:
> jabber:
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