From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.de>
Subject: Re: Shrinking number of devices on a RAID-10 (near 2) array
Date: Fri, 29 Aug 2014 13:53:12 +1000
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To: Andy Smith <andy@strugglers.net>
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On Mon, 25 Aug 2014 11:34:03 +0000 Andy Smith <andy@strugglers.net> wrote:

> Hi Neil,
>=20
> On Mon, Aug 25, 2014 at 09:26:14PM +1000, NeilBrown wrote:
> > What does "mdadm --examine" on one of the devices report now that it is=
 v1.0?
> >=20
> > Particularly interested in the "Unused Space :" line.
>=20
> /dev/sda3:
>           Magic : a92b4efc
>         Version : 1.0
>     Feature Map : 0x0
>      Array UUID : 3905b303:ca604b72:be5949c4:ab051b7a
>            Name : 2
>   Creation Time : Sun Jun  4 08:18:59 2006
>      Raid Level : raid10
>    Raid Devices : 6
>=20
>  Avail Dev Size : 618726528 (295.03 GiB 316.79 GB)
>      Array Size : 928089792 (885.10 GiB 950.36 GB)
>    Super Offset : 618727392 sectors
>    Unused Space : before=3D0 sectors, after=3D864 sectors
>           State : active
>     Device UUID : e30176be:81a57e84:1f2aa206:9515150f
>=20
>     Update Time : Sun Aug 24 14:29:15 2014
>        Checksum : bd599c72 - correct
>          Events : 1
>=20
>          Layout : near=3D2
>      Chunk Size : 64K
>=20
>    Device Role : Active device 5
>    Array State : AAAAAA ('A' =3D=3D active, '.' =3D=3D missing, 'R' =3D=
=3D replacing)
>=20
> All other devices report same (apart from UUID/checksum/role).

'after=3D864' should be plenty.

mdadm writes '128' to 'new_offset'
This is bigger than 'data_offset' (which must be zero, or it would have been
reported), mddev->dev_sectors is 618726528 while rdev->sectors is 618727392
(difference is 864), so=20
		if (new_offset - rdev->data_offset
		    + mddev->dev_sectors > rdev->sectors)
cannot return 'true'.  Yet it seems that it does.

Ahh.. somewhere else returns -E2BIG:

	if (mddev->pers && mddev->persistent &&
	    !super_types[mddev->major_version]
	    .allow_new_offset(rdev, new_offset))
		return -E2BIG;

But super_1_allow_new_offset always succeeds if new_offset >
rdev->data_offset, so that cannot be the problem.


I know.  rdev->sectors isn't "Super Offset", it is only "Avail Dev Size".
You need to
  echo 618727392 > /sys/block/md2/md/dev-sda3/size
and same for the other devices.

I looks like I need to get mdadm to be more clever when it gets -E2BIG.
Can you check that the above works?

Thanks,
NeilBrown


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