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

[yizhan <yizhan@redhat.com>]

On 01/27/2016 06:03 AM, NeilBrown wrote:
> On Tue, Jan 26 2016, yizhan wrote:
>
>> On 10/02/2015 03:55 PM, Neil Brown wrote:
>>> Yi Zhang <yizhan@redhat.com> 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.
> If, after stopping md127, you try
>
>    mdadm -I /dev/md0
>
> again it will start /dev/md127 again.  This is what udev does which
> causes md127 to appear in the first place.
>
> NeilBrown
Thanks Neil
I have tried 'mdadm -I /dev/md0', the /dev/md127 start again

Yi
>
>> 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