How to update homehost of an existing raid component

How to update homehost of an existing raid component

[Pavel Hofman]

Hi,

Please is there a way to update a homehost value for a specific raid
component?

md7 is raid1 composed of md5 and md6. UUID of md7 is listed in mdadm.conf:

ARRAY /dev/md7 level=raid1 num-devices=2 metadata=01.00
UUID=dde16cd5:2e17c743:fcc7926c:fcf5081e


Every time I reboot, md7 is auto assembled only from md5. When running
manually, I get

mdadm  --verbose -A /dev/md7  --scan
...
mdadm: /dev/md6 misses out due to wrong homehost
...


Indeed, all the raid components (there are many more belonging to
different raids on my machine) list the "local to host orfeus" homehost,
such as:

orfeus:~# mdadm --examine /dev/md5
/dev/md5:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : dde16cd5:2e17c743:fcc7926c:fcf5081e
           Name : orfeus:7  (local to host orfeus)
  Creation Time : Wed Jan 19 21:36:19 2011
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 4356361184 (2077.27 GiB 2230.46 GB)
     Array Size : 4356361184 (2077.27 GiB 2230.46 GB)
   Super Offset : 4356361440 sectors
          State : clean
    Device UUID : a4973bb6:2cd83805:ba441193:56321f9b

    Update Time : Mon Mar 19 02:36:33 2012
       Checksum : 7b8eeffd - correct
         Events : 11853346


   Device Role : Active device 1
   Array State : AA ('A' == active, '.' == missing)


While the md6 has the homehost different:
orfeus:~# mdadm --examine /dev/md6
/dev/md6:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : dde16cd5:2e17c743:fcc7926c:fcf5081e
           Name : 'orfeus':7
  Creation Time : Thu Jun 17 22:51:47 2010
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 4356361184 (2077.27 GiB 2230.46 GB)
     Array Size : 4356361184 (2077.27 GiB 2230.46 GB)
   Super Offset : 4356361440 sectors
          State : clean
    Device UUID : 9144c9ad:8ee3ed37:69b53956:03bebdd6

    Update Time : Mon Mar 19 02:36:33 2012
       Checksum : 94c11ff3 - correct
         Events : 11853346


   Device Role : Active device 0
   Array State : AA ('A' == active, '.' == missing)


There is no "local to host orfeus" in homehost of md6. Otherwise, the
array UUID fits that of md7. It was added after last reboot when the
array failed to assemble automatically.

Following the man page, I tried running

mdadm --verbose -A /dev/md7 --update=homehost --scan

with no difference. Unfortunately I was not able to find how to change
the homehost of md6 to be local to orfeus. I do not want to force adding
md6 to the array and go through the whole rebuild since the data
themselves are OK.


Thanks a lot for any hints and help.

Best regards,


Pavel.

Re: How to update homehost of an existing raid component

[John Robinson]

On 19/03/2012 09:58, Pavel Hofman wrote:
> Hi,
>
> Please is there a way to update a homehost value for a specific raid
> component?

I don't think you need to.

[...]
> mdadm --verbose -A /dev/md7 --update=homehost --scan
>
> with no difference. Unfortunately I was not able to find how to change
> the homehost of md6 to be local to orfeus. I do not want to force adding
> md6 to the array and go through the whole rebuild since the data
> themselves are OK.

I don't think --assemble --scan will include /dev/md6 if the homehost 
doesn't match :-(

Try mdadm --verbose --assemble /dev/md7 --update=homehost /dev/md5 /dev/md6

And if that doesn't do the business, specify --homehost=orfeus

Cheers,

John.

Re: How to update homehost of an existing raid component

[Pavel Hofman]

Dne 19.3.2012 17:46, John Robinson napsal(a):
> On 19/03/2012 09:58, Pavel Hofman wrote:
>> Hi,
>>
>> Please is there a way to update a homehost value for a specific raid
>> component?
> 
> I don't think you need to.
> 
> [...]
>> mdadm --verbose -A /dev/md7 --update=homehost --scan
>>
>> with no difference. Unfortunately I was not able to find how to change
>> the homehost of md6 to be local to orfeus. I do not want to force adding
>> md6 to the array and go through the whole rebuild since the data
>> themselves are OK.
> 
> 

Hi John,

Thanks a lot for your answer. Unfortunately both commands keep returning
the same result:

orfeus:~# mdadm --verbose --assemble /dev/md7 --update=homehost /dev/md5
/dev/md6
mdadm: looking for devices for /dev/md7
mdadm: /dev/md6 misses out due to wrong homehost
mdadm: /dev/md5 is identified as a member of /dev/md7, slot 1.
mdadm: no uptodate device for slot 0 of /dev/md7
mdadm: added /dev/md5 to /dev/md7 as 1
mdadm: /dev/md7 assembled from 1 drive - need all 2 to start it (use
--run to insist).


> 
> And if that doesn't do the business, specify --homehost=orfeus

orfeus:~# mdadm --verbose --assemble /dev/md7 --update=homehost
--homehost=orfeus /dev/md5 /dev/md6
mdadm: looking for devices for /dev/md7
mdadm: /dev/md6 misses out due to wrong homehost
mdadm: /dev/md5 is identified as a member of /dev/md7, slot 1.
mdadm: no uptodate device for slot 0 of /dev/md7
mdadm: added /dev/md5 to /dev/md7 as 1
mdadm: /dev/md7 assembled from 1 drive - need all 2 to start it (use
--run to insist).

orfeus:~# mdadm --version
mdadm - v3.1.4 - 31st August 2010

orfeus:~# uname -a
Linux orfeus 2.6.26-bpo.1-amd64 #1 SMP Sat Sep 20 10:26:59 UTC 2008
x86_64 GNU/Linux


Since I need the server working (it is a company central backup server),
I forced starting md7 in degraded mode by including the --run parameter
and re-added md6 afterwards. Since both components carry the
write-intent bitmap and the degraded array was not accessed in the
meantime, md6 was re-added without any synchronization.

Still, md6 is not local to orfeus:

orfeus:~# mdadm --examine /dev/md6
/dev/md6:
....
           Name : 'orfeus':7
...

While md5 is:

orfeus:~# mdadm --examine /dev/md5
/dev/md5:
....
           Name : orfeus:7  (local to host orfeus)
....


Next time the problem will arise again. No idea how to force md6 to
become local. It looks as if md6 was created in some preliminary stage
of homehost support and its current homehost format is not supported by
the mdadm utils. Just my guess though.

John, once more thank you for your invaluable help.

Regards,


Pavel.

Re: How to update homehost of an existing raid component

[NeilBrown]

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On Mon, 19 Mar 2012 10:58:57 +0100 Pavel Hofman <pavel.hofman@ivitera.com>
wrote:

> Hi,
> 
> Please is there a way to update a homehost value for a specific raid
> component?
> 
> md7 is raid1 composed of md5 and md6. UUID of md7 is listed in mdadm.conf:
> 
> ARRAY /dev/md7 level=raid1 num-devices=2 metadata=01.00
> UUID=dde16cd5:2e17c743:fcc7926c:fcf5081e
> 
> 
> Every time I reboot, md7 is auto assembled only from md5. When running
> manually, I get
> 
> mdadm  --verbose -A /dev/md7  --scan
> ...
> mdadm: /dev/md6 misses out due to wrong homehost
> ...
> 

There is something very strange here.
md5 and md6 look to some extent like different parts of the same RAID1.
They have the same Array UUID, the same "Update Time" and the same "Events"
counter.
However they have different "Creation Time" (19/Jan/2011 vs 17/Jun/2010) and
different names ("orfeus:7" vs "'orpheus':7").

I cannot imagine how that would happen.

mdadm notices they are different so it cannot use them both.  It chooses md5
over md6 as md5 has the 'correct' homehost name.

Your best bet would be to re-create the array so it gets good clean metadata.

mdadm -S /dev/md7
mdadm -C /dev/md7 -l1 -n2 --assume-clean --metadata=1.0 /dev/md6 /dev/md5

should do it.  If you want to keep the same uuid, add
   --uuid=dde16cd5:2e17c743:fcc7926c:fcf5081e

to that command.

--update=homehost only works when assembling, and updates the homehost for
all members of the array.  The would work if the create times were the same,
but a they are different, mdadm thinks they are different arrays.

NeilBrown


> 
> Indeed, all the raid components (there are many more belonging to
> different raids on my machine) list the "local to host orfeus" homehost,
> such as:
> 
> orfeus:~# mdadm --examine /dev/md5
> /dev/md5:
>           Magic : a92b4efc
>         Version : 1.0
>     Feature Map : 0x0
>      Array UUID : dde16cd5:2e17c743:fcc7926c:fcf5081e
>            Name : orfeus:7  (local to host orfeus)
>   Creation Time : Wed Jan 19 21:36:19 2011
>      Raid Level : raid1
>    Raid Devices : 2
> 
>  Avail Dev Size : 4356361184 (2077.27 GiB 2230.46 GB)
>      Array Size : 4356361184 (2077.27 GiB 2230.46 GB)
>    Super Offset : 4356361440 sectors
>           State : clean
>     Device UUID : a4973bb6:2cd83805:ba441193:56321f9b
> 
>     Update Time : Mon Mar 19 02:36:33 2012
>        Checksum : 7b8eeffd - correct
>          Events : 11853346
> 
> 
>    Device Role : Active device 1
>    Array State : AA ('A' == active, '.' == missing)
> 
> 
> While the md6 has the homehost different:
> orfeus:~# mdadm --examine /dev/md6
> /dev/md6:
>           Magic : a92b4efc
>         Version : 1.0
>     Feature Map : 0x0
>      Array UUID : dde16cd5:2e17c743:fcc7926c:fcf5081e
>            Name : 'orfeus':7
>   Creation Time : Thu Jun 17 22:51:47 2010
>      Raid Level : raid1
>    Raid Devices : 2
> 
>  Avail Dev Size : 4356361184 (2077.27 GiB 2230.46 GB)
>      Array Size : 4356361184 (2077.27 GiB 2230.46 GB)
>    Super Offset : 4356361440 sectors
>           State : clean
>     Device UUID : 9144c9ad:8ee3ed37:69b53956:03bebdd6
> 
>     Update Time : Mon Mar 19 02:36:33 2012
>        Checksum : 94c11ff3 - correct
>          Events : 11853346
> 
> 
>    Device Role : Active device 0
>    Array State : AA ('A' == active, '.' == missing)
> 
> 
> There is no "local to host orfeus" in homehost of md6. Otherwise, the
> array UUID fits that of md7. It was added after last reboot when the
> array failed to assemble automatically.
> 
> Following the man page, I tried running
> 
> mdadm --verbose -A /dev/md7 --update=homehost --scan
> 
> with no difference. Unfortunately I was not able to find how to change
> the homehost of md6 to be local to orfeus. I do not want to force adding
> md6 to the array and go through the whole rebuild since the data
> themselves are OK.
> 
> 
> Thanks a lot for any hints and help.
> 
> Best regards,
> 
> 
> Pavel.
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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


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Re: How to update homehost of an existing raid component

[Pavel Hofman]

Dne 19.3.2012 22:28, NeilBrown napsal(a):
> On Mon, 19 Mar 2012 10:58:57 +0100 Pavel Hofman <pavel.hofman@ivitera.com>
> wrote:
> 
>> Hi,
>>
>> Please is there a way to update a homehost value for a specific raid
>> component?
>>
>> md7 is raid1 composed of md5 and md6. UUID of md7 is listed in mdadm.conf:
>>
>> ARRAY /dev/md7 level=raid1 num-devices=2 metadata=01.00
>> UUID=dde16cd5:2e17c743:fcc7926c:fcf5081e
>>
>>
>> Every time I reboot, md7 is auto assembled only from md5. When running
>> manually, I get
>>
>> mdadm  --verbose -A /dev/md7  --scan
>> ...
>> mdadm: /dev/md6 misses out due to wrong homehost
>> ...
>>
> 
> There is something very strange here.
> md5 and md6 look to some extent like different parts of the same RAID1.
> They have the same Array UUID, the same "Update Time" and the same "Events"
> counter.
> However they have different "Creation Time" (19/Jan/2011 vs 17/Jun/2010) and
> different names ("orfeus:7" vs "'orpheus':7").
> 
> I cannot imagine how that would happen.
> 
> mdadm notices they are different so it cannot use them both.  It chooses md5
> over md6 as md5 has the 'correct' homehost name.
> 
> Your best bet would be to re-create the array so it gets good clean metadata.
> 
> mdadm -S /dev/md7
> mdadm -C /dev/md7 -l1 -n2 --assume-clean --metadata=1.0 /dev/md6 /dev/md5
> 
> should do it.  If you want to keep the same uuid, add
>    --uuid=dde16cd5:2e17c743:fcc7926c:fcf5081e
> 

Neil, thanks a lot for your help. The command worked fine, now both md5
and md6 have the same name.

Regards,

Pavel.