On 04/23/2017 04:48 PM, Andreas Klauer wrote:
> On Sun, Apr 23, 2017 at 10:06:15PM +0800, Brad Campbell wrote:
>> Nobody seems to have mentioned the reshape issue.
>
> Good point.
>
> If it was mid-reshape you need two sets of overlays,
> create two RAIDs (one for each configuration), and
> then find the point where it converges.
>
>> If my reading of the code is correct (and my memory
>> is any good), simply adding a disk to a raid5 on a
>> recent enough kernel should make the resync go backwards.
>
> Doesn't it cut the offset by half and grow forwards...?
>
> With growing a disk that should give you a segment where
> data is identical for both 5-disk and 6-disk RAID-5.
> And that's where you join them using dmsetup linear.
>
> Before:
>
> /dev/loop0:
> Magic : a92b4efc
> Version : 1.2
> Feature Map : 0x1
> Array UUID : 4611f41b:0464e815:8b6f9cfe:b29c56fd
> Name : EIS:42 (local to host EIS)
> Creation Time : Sun Apr 23 16:44:59 2017
> Raid Level : raid5
> Raid Devices : 5
>
> Avail Dev Size : 11720783024 (5588.90 GiB 6001.04 GB)
> Array Size : 23441565696 (22355.62 GiB 24004.16 GB)
> Used Dev Size : 11720782848 (5588.90 GiB 6001.04 GB)
> Data Offset : 262144 sectors
> Super Offset : 8 sectors
> Unused Space : before=262064 sectors, after=176 sectors
> State : clean
> Device UUID : acd8d9fd:7b7cf9a0:f63369d1:907ffa66
>
> Internal Bitmap : 8 sectors from superblock
> Update Time : Sun Apr 23 16:44:59 2017
> Bad Block Log : 512 entries available at offset 32 sectors
> Checksum : f89bdc5 - correct
> Events : 2
>
> Layout : left-symmetric
> Chunk Size : 512K
>
> Device Role : Active device 0
> Array State : AAAAA ('A' == active, '.' == missing, 'R' == replacing)
>
> After/During grow:
>
> /dev/loop0:
> Magic : a92b4efc
> Version : 1.2
> Feature Map : 0x45
> Array UUID : 4611f41b:0464e815:8b6f9cfe:b29c56fd
> Name : EIS:42 (local to host EIS)
> Creation Time : Sun Apr 23 16:44:59 2017
> Raid Level : raid5
> Raid Devices : 6
>
> Avail Dev Size : 11720783024 (5588.90 GiB 6001.04 GB)
> Array Size : 29301957120 (27944.52 GiB 30005.20 GB)
> Used Dev Size : 11720782848 (5588.90 GiB 6001.04 GB)
> Data Offset : 262144 sectors
> | New Offset : 257024 sectors
> Super Offset : 8 sectors
> State : clean
> Device UUID : acd8d9fd:7b7cf9a0:f63369d1:907ffa66
>
> Internal Bitmap : 8 sectors from superblock
> | Reshape pos'n : 1472000 (1437.50 MiB 1507.33 MB)
> | Delta Devices : 1 (5->6)
>
> Update Time : Sun Apr 23 16:45:38 2017
> Bad Block Log : 512 entries available at offset 32 sectors
> Checksum : fbd9a55 - correct
> Events : 30
>
> Layout : left-symmetric
> Chunk Size : 512K
>
> Device Role : Active device 0
> Array State : AAAAAA ('A' == active, '.' == missing, 'R' == replacing)
>
> Basically you have to know the New Offset
> (search first 128M of your drives for filesystem headers, that should be it)
Let's see if I understand you correctly:
* I try to find 0x53EF (ext4 magic) within the first 128M of
/dev/sd[abcde]. Not after? This will be an indication of my "New
Offset". I need to adjust the offset a bit since the ext4 magic is
located at 0x438 offset.
> and then guess the Reshape pos'n by comparing raw data at offset X
> (find non-zero data at identical offsets for both raid sets)
* I create a 5 and a 6 drive raid set and try to find an offset where
they both carry the same raw data. With some overlays, I should be able
to create both these raids at the same time, correct?
>
> Regards
> Andreas Klauer
>
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