Re: raid0: device does not exist with examine and scan

[Nigel Croxon <ncroxon@redhat.com>]

On 07/27/2017 01:17 PM, Nigel Croxon wrote:
> On 07/27/2017 01:07 PM, Wols Lists wrote:
>> On 27/07/17 17:11, Nigel Croxon wrote:
>>>
>>> Hello all,
>>>
>>> The device name referenced in the mdadm --examine --scan does not exist
>>> when using metadata=1.2 and --name on the creation.
>>> I am using metadata 0.9 as a bases to test against 1.2.
>>> Am I fighting a udev rule? Did the symlink from /dev/md/TEST_MD to
>>> /dev/md0 disappear?
>>>
>>>
>>> If I start with METADATA=0.9 and specifying a --name
>>>
>>> # mdadm --create --verbose /dev/md0 --level=0 --metadata=0.9
>>> --raid-devices=2 --name=TEST_MD /dev/sdd /dev/sde
>>>
>>> with METADATA=0.9, there is no NAME field printed on DETAIL
>>
>> I don't think 0.9 metadata supports names ...
>>>
>>> # mdadm -D /dev/md0
>>> /dev/md0:
>>>            Version : 0.90
>>>      Creation Time : Thu Jul 27 10:36:02 2017
>>>         Raid Level : raid0
>>>         Array Size : 293045760 (279.47 GiB 300.08 GB)
>>>       Raid Devices : 2
>>>      Total Devices : 2
>>>    Preferred Minor : 0
>>>        Persistence : Superblock is persistent
>>>
>>>        Update Time : Thu Jul 27 10:36:02 2017
>>>              State : clean
>>>     Active Devices : 2
>>>    Working Devices : 2
>>>     Failed Devices : 0
>>>      Spare Devices : 0
>>>
>>>         Chunk Size : 512K
>>>
>>> Consistency Policy : none
>>>
>>>               UUID : 623d8bac:8819491b:e9034e5d:acd14f01
>>>             Events : 0.1
>>>
>>>     Number   Major   Minor   RaidDevice State
>>>        0       8       48        0      active sync   /dev/sdd
>>>        1       8       64        1      active sync   /dev/sde
>>>
>>>
>>> The --examine --scan shows /dev/md0, and not /dev/md/TEST_MD.
>>> # mdadm --examine --scan
>>> ARRAY /dev/md0 UUID=65cb66eb:d8a0d9ff:85609b40:89383835
>>>
>>>
>>> Next, change the METADATA=1.2 and specifying a --name
>>> # mdadm --create --verbose /dev/md0 --level=0 --metadata=1.2
>>> --raid-devices=2 --name=TEST_MD /dev/sdd /dev/sde
>>>
>>> With METADATA=1.2, there is a NAME field printed:
>>> thinkstation:TEST_MD  (local to host thinkstation)
>>>
>>> # mdadm -D /dev/md0
>>> /dev/md0:
>>>            Version : 1.2
>>>      Creation Time : Thu Jul 27 11:13:02 2017
>>>         Raid Level : raid0
>>>         Array Size : 292784128 (279.22 GiB 299.81 GB)
>>>       Raid Devices : 2
>>>      Total Devices : 2
>>>        Persistence : Superblock is persistent
>>>
>>>        Update Time : Thu Jul 27 11:13:02 2017
>>>              State : clean
>>>     Active Devices : 2
>>>    Working Devices : 2
>>>     Failed Devices : 0
>>>      Spare Devices : 0
>>>
>>>         Chunk Size : 512K
>>>
>>> Consistency Policy : none
>>>
>>>               Name : thinkstation:TEST_MD  (local to host thinkstation)
>>>               UUID : 591d68eb:5182a6e2:ead93be0:812f7fc6
>>>             Events : 0
>>>
>>>     Number   Major   Minor   RaidDevice State
>>>        0       8       48        0      active sync   /dev/sdd
>>>        1       8       64        1      active sync   /dev/sde
>>>
>>> The --examine --scan is shows /dev/md/TEST_MD and not /dev/md0.
>>>
>>> # mdadm --examine --scan
>>> ARRAY /dev/md/TEST_MD  metadata=1.2
>>> UUID=413a8ca9:a1edb21b:9eb8876d:784349ed name=thinkstation:TEST_MD
>>>
>>> This problem is, /dev/md/TEST_MD does not exist. /dev/md0 does.
>>
>> Is the array running? This is an educated guess on my part, but I think
>> it's running the array that creates the symlink.
>>>
> 
> # mdadm --create --verbose /dev/md0 --level=0 --metadata=1.2
> --raid-devices=2 --name=TEST_MD /dev/sdd /dev/sde
> mdadm: chunk size defaults to 512K
> mdadm: array /dev/md0 started.
> 
> # cat /proc/mdstat
> Personalities : [raid0]
> md0 : active raid0 sde[1] sdd[0]
>       292784128 blocks super 1.2 512k chunks
> 
> unused devices: <none>
> 
> # mdadm --examine --scan
> ARRAY /dev/md/TEST_MD  metadata=1.2
> UUID=fff9f89d:62dcc596:665386ca:d19f2487 name=thinkstation:TEST_MD
> 
> # ls /dev/md/
> ls: cannot access /dev/md/: No such file or directory
> 
> 
>>> mdadm --version
>>> mdadm - v4.0-158-gcb91230 - 2017-07-10
>>>
>>> Am I fighting udev rules?
>>>
>> Cheers,
>> Wol
>>
>>

Looks like I'm all set.

1) Reboot - and the symlink will be there.
or
2) stop the device and reassemble with -I

This is how the udev rules do it.

-Nigel