# Re: md127 auto created when use "-B" to build a legacy array without superblocks

- From: yizhan \<hidden\>
- Date: 2016-01-26 08:24:01 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2016/01/6631459
- Thread: https://ratatoskr.run/linux-raid/2015/09/6630332/t.md

```text


On 10/02/2015 03:55 PM, Neil Brown wrote:
> Yi Zhang [ref] writes:
>
>> Hi Neil
>>
>> When testing 00raid1, found the md127 auto created when use "-B" to build a legacy array without superblocks, is it reasonable?
> This happens because udev notices a new device has appeared, looks
> inside it, sees that it could be part of an md array, and so runs
> "mdadm --incremental" on it.
Hi Neil
I tried the mdadm --incremental, but it doesn't work, below is the operation.
# mdadm -D /dev/md0
/dev/md0:
        Version :
  Creation Time : Tue Jan 26 03:16:17 2016
     Raid Level : raid1
     Array Size : 2097152 (2.00 GiB 2.15 GB)
  Used Dev Size : 2097152 (2.00 GiB 2.15 GB)
   Raid Devices : 2
  Total Devices : 2

          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

    Number   Major   Minor   RaidDevice State
       0       7        0        0      active sync   /dev/loop0
       1       7        1        1      active sync   /dev/loop1
# mdadm -D /dev/md127
/dev/md127:
        Version : 1.2
     Raid Level : raid0
  Total Devices : 1
    Persistence : Superblock is persistent

          State : inactive

           Name : 0
           UUID : 13ada118:129135ff:686de7b7:4cb71d6d
         Events : 17

    Number   Major   Minor   RaidDevice

       -       9        0        -        /dev/md0
# mdadm -I /dev/md127
mdadm: /dev/md127 is not part of an md array.
# mdadm -I /dev/md0
mdadm: cannot reopen /dev/md0: Device or resource busy.

After I stopped md127, the md0 can be used again.

Thanks
Yi
> Sometimes we want udev to do that.  Sometimes we don't.
> There is no easy way for udev to know what we want.
>
> NeilBrown
>
>
>> pls check below detailed info:
>>
>> + mdadm -CR /dev/md0 --level=raid1 -n3 /dev/loop0 /dev/loop1 /dev/loop2
>> mdadm: /dev/loop0 appears to contain an ext2fs file system
>>         size=58368K  mtime=Thu Jan  1 08:00:00 1970
>> mdadm: Note: this array has metadata at the start and
>>      may not be suitable as a boot device.  If you plan to
>>      store '/boot' on this device please ensure that
>>      your boot-loader understands md/v1.x metadata, or use
>>      --metadata=0.90
>> mdadm: /dev/loop1 appears to contain an ext2fs file system
>>         size=38912K  mtime=Thu Jan  1 08:00:00 1970
>> mdadm: Defaulting to version 1.2 metadata
>> mdadm: array /dev/md0 started.
>> + mdadm --wait /dev/md0
>> + cat /proc/mdstat
>> Personalities : [raid6] [raid5] [raid4] [raid1]
>> md0 : active raid1 loop2[2] loop1[1] loop0[0]
>>        19968 blocks super 1.2 [3/3] [UUU]
>>        
>> unused devices: <none>
>> + mdadm -S /dev/md0
>> mdadm: stopped /dev/md0
>> + mdadm -B /dev/md0 -l raid1 -n2 /dev/loop0 /dev/loop1
>> mdadm: array /dev/md0 built and started.
>> + sleep 2
>> + cat /proc/mdstat
>> Personalities : [raid6] [raid5] [raid4] [raid1]
>> md127 : inactive md0[0](S)
>>        19968 blocks super 1.2
>>         
>> md0 : active raid1 loop1[1] loop0[0]
>>        20000 blocks super non-persistent [2/2] [UU]
>>        
>> unused devices: <none>
>> [root@dhcp-12-171 bug]# uname -r
>> 4.2.0
>> [root@dhcp-12-171 bug]# mdadm -D /dev/md0
>> /dev/md0:
>>          Version :
>>    Creation Time : Mon Sep  7 20:21:20 2015
>>       Raid Level : raid1
>>       Array Size : 20000 (19.53 MiB 20.48 MB)
>>    Used Dev Size : 20000 (19.53 MiB 20.48 MB)
>>     Raid Devices : 2
>>    Total Devices : 2
>>
>>            State : clean
>>   Active Devices : 2
>> Working Devices : 2
>>   Failed Devices : 0
>>    Spare Devices : 0
>>
>>      Number   Major   Minor   RaidDevice State
>>         0       7        0        0      active sync   /dev/loop0
>>         1       7        1        1      active sync   /dev/loop1
>> [root@dhcp-12-171 bug]# mdadm -D /dev/md127
>> /dev/md127:
>>          Version : 1.2
>>       Raid Level : raid0
>>    Total Devices : 1
>>      Persistence : Superblock is persistent
>>
>>            State : inactive
>>
>>             Name : dhcp-12-171.nay.redhat.com:0  (local to host dhcp-12-171.nay.redhat.com)
>>             UUID : 40ace956:a9dd0793:f4984d2b:8431b92b
>>           Events : 17
>>
>>      Number   Major   Minor   RaidDevice
>>
>>         -       9        0        -        /dev/md0
>>
>> Best Regards,
>>    Yi Zhang

```