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)
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)
Regards
Andreas Klauer
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