Re: convert raid10 to raid0

["Tóth Csaba" <csaba.toth@i3rendszerhaz.hu>]

Hey there,

thanks for help, we modified the mdadm's source code, and everything
worked fine. You saved us!! :)))

best wishes,
Csaba



2010.07.09. 1:15 keltezéssel, Neil Brown írta:
> On Thu, 08 Jul 2010 10:27:46 +0200
> Tóth Csaba <csaba.toth@i3rendszerhaz.hu> wrote:
> 
>> 2010.07.08. 9:58 keltezéssel, Tóth Csaba írta:
>>> 2010.07.08. 0:50 keltezéssel, Neil Brown írta:
>>>> Then after you create the raid0, use the same command
>>>>    mdadm -E /dev/sdc6
>>>> to check the Data Offset again and make sure it is the same.
>>>> I suspect it will be, so everything will be fine.
>>>> However if it isn't don't try to access the array.   Post the details and I'll
>>>> figure out what to do next.
>>>>
>>>
>>> It doesn't work, [...]
>>
>> forget to explain what i did: my idea was to create a new array with
>> --assume-clean, than kick out the knowed bad members:
>>
>> minerva data-bck # mdadm --create /dev/md5 --assume-clean --metadata=1.1
>> --level=10 --raid-devices=4 /dev/sdb6 /dev/sda6 /dev/sdc6 /dev/sdd6
>> mdadm: /dev/sdb6 appears to be part of a raid array:
>>     level=raid10 devices=4 ctime=Thu Jul  8 09:47:43 2010
>> mdadm: /dev/sda6 appears to be part of a raid array:
>>     level=raid10 devices=4 ctime=Thu Jul  8 09:47:43 2010
>> mdadm: /dev/sdc6 appears to be part of a raid array:
>>     level=raid10 devices=4 ctime=Thu Jul  8 09:47:43 2010
>> mdadm: /dev/sdd6 appears to be part of a raid array:
>>     level=raid10 devices=4 ctime=Thu Jul  8 09:47:43 2010
>> Continue creating array? yes
>> mdadm: array /dev/md5 started.
>> minerva data-bck #
>> minerva data-bck # man mdadm
>> minerva data-bck # mdadm /dev/md5 --fail /dev/sda6 --fail /dev/sdc6
>> mdadm: set /dev/sda6 faulty in /dev/md5
>> mdadm: set /dev/sdc6 faulty in /dev/md5
>> minerva data-bck # cat /proc/mdstat
>> Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5]
>> [raid4] [multipath] [faulty]
>> md5 : active raid10 sdd6[3] sdc6[2](F) sda6[1](F) sdb6[0]
>>       1434617856 blocks super 1.1 512K chunks 2 near-copies [4/2] [U__U]
>>
>>
>> this is exactly the same layout as i had before, just the data offset
>> doesn't match.
>>
> 
> OK, there are two things you can do - both might be interesting.
> 
> 1/ You can temporarily adjust the data offset by writing directly to sysfs.
> 
>    cd /sys/block/md5/md
>    echo inactive > array_state
>    echo 592 > dev-sdb6/offset
>    echo 264 > dev-sdd6/offset
>    echo readonly > array_state
> 
>    Now you should be able to examine you data and assure yourself that it is
>    all there.  However this doesn't change the metadata so when you stop and
>    restart the array the offset will be back where it started.
> 
> 2/ hack the code in 'super1.c' and re-create the array.
>    in write_init_super1, after the 'switch' statement that set data_offset,
>    put
>      if (strcmp(di->devname, "/dev/sdb6") ==0) sb->data_offset =  __cpu_to_le64(592);
>      if (strcmp(di->devname, "/dev/sdd6") ==0) sb->data_offset =  __cpu_to_le64(264);
> 
>    ofcourse you should check that code and make sure you agree that I have
>    written it correctly.
> 
> I plan to enhance mdadm so you can 'recreate' and array - it then takes
> offsets etc out of current metadata and only changes the bits you ask it to
> change.  Had I done this already this would have been a lot easier for you,
> but unfortunately I haven't.
> 
> good luck,
> NeilBrown
> 
> 

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