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

[Neil Brown <neilb@suse.com>]

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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.

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

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