convert raid10 to raid0

convert raid10 to raid0

[Tóth Csaba]

Hey List,

i have a serious problem: have a file server with 4 disk (4x750GB),
using them in a software RAID10 array. One of the HDDs have a bad sector
(because some administration problems, i cannot replace them), and the
motherboard sometimes drops the connection with two HDDs. Not with the
same as the bad sector has, but with a resync i always managed the
problem. But now 3 drive form the RAID10 array dropped.

In the past the sdc6 and the sdd6 partitions were the partitions i
resynced the others, so i know exactly where to look for the proper
datas. Can i use them as a RAID0 array somehow?
In past mdadm warning letters i saw the config:

Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5]
[raid4] [multipath] [faulty]
md5 : active raid10 sdc6[0] sdd6[3] sdb6[1](F) sda6[2](F)
      1434619904 blocks super 1.1 512K chunks 2 near-copies [4/2] [U__U]

md1 : active raid1 sdb5[0] sdc5[1]
      14763635 blocks super 1.1 [2/2] [UU]

md0 : active raid1 sdd5[0] sda5[2](F)
      14659200 blocks [2/1] [U_]

unused devices: <none>


Now i have:

minerva ~ # cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5]
[raid4] [multipath] [faulty]
md5 : inactive sdd6[3]
      717310119 blocks super 1.1

md1 : active raid1 sdc5[0] sdb5[1]
      14763635 blocks super 1.1 [2/2] [UU]

md0 : active raid1 sda5[1] sdd5[0]
      14659200 blocks [2/2] [UU]

unused devices: <none>
minerva ~ # mdadm --detail /dev/md5
/dev/md5:
        Version : 1.1
  Creation Time : Thu Nov 26 14:50:07 2009
     Raid Level : raid10
  Used Dev Size : 717309952 (684.08 GiB 734.53 GB)
   Raid Devices : 4
  Total Devices : 1
    Persistence : Superblock is persistent

    Update Time : Wed Jul  7 10:34:32 2010
          State : active, FAILED, Not Started
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0

         Layout : near=2
     Chunk Size : 512K

           Name : minerva:5  (local to host minerva)
           UUID : a73f5902:accc2488:aecfdc14:05a6e2f4
         Events : 3981420

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       0        0        1      removed
       2       0        0        2      removed
       3       8       54        3      active sync   /dev/sdd6




If i try to add sdc6 to the md5 array it fails, because it tries to add
as a fifth device:

minerva ~ # mdadm /dev/md5 -a /dev/sdc6
mdadm: add new device failed for /dev/sdc6 as 4: Invalid argument



Please help, i don't want to destroy the datas, and i have never job
with RAID10 under linux.

thanks in advance,
regards,
Csaba

Re: convert raid10 to raid0

[Neil Brown]

On Wed, 07 Jul 2010 21:29:49 +0200
Tóth Csaba <csaba.toth@i3rendszerhaz.hu> wrote:

> Hey List,
> 
> i have a serious problem: have a file server with 4 disk (4x750GB),
> using them in a software RAID10 array. One of the HDDs have a bad sector
> (because some administration problems, i cannot replace them), and the
> motherboard sometimes drops the connection with two HDDs. Not with the
> same as the bad sector has, but with a resync i always managed the
> problem. But now 3 drive form the RAID10 array dropped.
> 
> In the past the sdc6 and the sdd6 partitions were the partitions i
> resynced the others, so i know exactly where to look for the proper
> datas. Can i use them as a RAID0 array somehow?

It should be sufficient to:
  mdadm -S /dev/md5
  mdadm -C /dev/md5 --level raid0 --raid-devices 2 --chunk 512 \
      --metadata=1.1 /dev/sdc6 /dev/sdd6

to get your data available.
There is a possible small complication though.  If you use a different
version of mdadm to the one you used to create the array at first, it might
choose a different 'data offset'.
To be sure this doesn't happen, use

 mdadm -E /dev/sdc6

and take note of the "Data Offset".  It would probably be a good idea to keep
a copy of "mdadm -E" of all of the devices, just to be on the same side.

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.

NeilBrown


> In past mdadm warning letters i saw the config:
> 
> Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5]
> [raid4] [multipath] [faulty]
> md5 : active raid10 sdc6[0] sdd6[3] sdb6[1](F) sda6[2](F)
>       1434619904 blocks super 1.1 512K chunks 2 near-copies [4/2] [U__U]
> 
> md1 : active raid1 sdb5[0] sdc5[1]
>       14763635 blocks super 1.1 [2/2] [UU]
> 
> md0 : active raid1 sdd5[0] sda5[2](F)
>       14659200 blocks [2/1] [U_]
> 
> unused devices: <none>
> 
> 
> Now i have:
> 
> minerva ~ # cat /proc/mdstat
> Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5]
> [raid4] [multipath] [faulty]
> md5 : inactive sdd6[3]
>       717310119 blocks super 1.1
> 
> md1 : active raid1 sdc5[0] sdb5[1]
>       14763635 blocks super 1.1 [2/2] [UU]
> 
> md0 : active raid1 sda5[1] sdd5[0]
>       14659200 blocks [2/2] [UU]
> 
> unused devices: <none>
> minerva ~ # mdadm --detail /dev/md5
> /dev/md5:
>         Version : 1.1
>   Creation Time : Thu Nov 26 14:50:07 2009
>      Raid Level : raid10
>   Used Dev Size : 717309952 (684.08 GiB 734.53 GB)
>    Raid Devices : 4
>   Total Devices : 1
>     Persistence : Superblock is persistent
> 
>     Update Time : Wed Jul  7 10:34:32 2010
>           State : active, FAILED, Not Started
>  Active Devices : 1
> Working Devices : 1
>  Failed Devices : 0
>   Spare Devices : 0
> 
>          Layout : near=2
>      Chunk Size : 512K
> 
>            Name : minerva:5  (local to host minerva)
>            UUID : a73f5902:accc2488:aecfdc14:05a6e2f4
>          Events : 3981420
> 
>     Number   Major   Minor   RaidDevice State
>        0       0        0        0      removed
>        1       0        0        1      removed
>        2       0        0        2      removed
>        3       8       54        3      active sync   /dev/sdd6
> 
> 
> 
> 
> If i try to add sdc6 to the md5 array it fails, because it tries to add
> as a fifth device:
> 
> minerva ~ # mdadm /dev/md5 -a /dev/sdc6
> mdadm: add new device failed for /dev/sdc6 as 4: Invalid argument
> 
> 
> 
> Please help, i don't want to destroy the datas, and i have never job
> with RAID10 under linux.
> 
> thanks in advance,
> regards,
> Csaba
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Re: convert raid10 to raid0

[Tóth Csaba]

Hi,

2010.07.08. 0:50 keltezéssel, Neil Brown írta:
> On Wed, 07 Jul 2010 21:29:49 +0200
> Tóth Csaba <csaba.toth@i3rendszerhaz.hu> wrote:
> 
>> Hey List,
>>
>> i have a serious problem: have a file server with 4 disk (4x750GB),
>> using them in a software RAID10 array. One of the HDDs have a bad sector
>> (because some administration problems, i cannot replace them), and the
>> motherboard sometimes drops the connection with two HDDs. Not with the
>> same as the bad sector has, but with a resync i always managed the
>> problem. But now 3 drive form the RAID10 array dropped.
>>
>> In the past the sdc6 and the sdd6 partitions were the partitions i
>> resynced the others, so i know exactly where to look for the proper
>> datas. Can i use them as a RAID0 array somehow?
> 
> It should be sufficient to:
>   mdadm -S /dev/md5
>   mdadm -C /dev/md5 --level raid0 --raid-devices 2 --chunk 512 \
>       --metadata=1.1 /dev/sdc6 /dev/sdd6
> 
> to get your data available.
> There is a possible small complication though.  If you use a different
> version of mdadm to the one you used to create the array at first, it might
> choose a different 'data offset'.
> To be sure this doesn't happen, use
> 
>  mdadm -E /dev/sdc6
> 
> and take note of the "Data Offset".  It would probably be a good idea to keep
> a copy of "mdadm -E" of all of the devices, just to be on the same side.
> 
> 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.
> 

i have made a small test case:

DTADIR=/mnt/data
MDF=/dev/md8

dd bs=512 count=180000 if=/dev/zero of=${DTADIR}/a
dd bs=512 count=180000 if=/dev/zero of=${DTADIR}/b
dd bs=512 count=180000 if=/dev/zero of=${DTADIR}/c
dd bs=512 count=180000 if=/dev/zero of=${DTADIR}/d

losetup /dev/loop0 ${DTADIR}/a
losetup /dev/loop1 ${DTADIR}/b
losetup /dev/loop2 ${DTADIR}/c
losetup /dev/loop3 ${DTADIR}/d

mdadm --create ${MDF} --level=10 --metadata=1.1 \
 --raid-devices=4 /dev/loop0 /dev/loop1 /dev/loop2 /dev/loop3
mkfs.ext4 ${MDF}

mkdir ${DTADIR}/tmp
mount ${MDF} ${DTADIR}/tmp
cp -a /etc ${DTADIR}/tmp
umount ${MDF}

mdadm -S ${MDF}
mdadm -C /dev/md5 --level raid0 --raid-devices 2 --chunk 512 \
--metadata=1.1 /dev/loop0 /dev/loop3

mount ${MDF} ${DTADIR}/tmp
ls -al ${DTADIR}/tmp

umount ${MDF}
mdadm -S ${MDF}
losetup --detach /dev/loop0 /dev/loop1 /dev/loop2 /dev/loop3



i used loop0 and loop3 to construct the raid0 array, because they were
at the same (0 and 3) position than the devices i had in my real raid10
array. so this should work, but not :(
but after i made a raid0 array, and than recreate the raid10 array it
worked well. can't i create a raid10 array with two drives?

regards,
Csaba
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Re: convert raid10 to raid0

[Tóth Csaba]

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, and the data offsets are different (in the mean time i
figured out that i made a mistake, and not sdc6 but sdb6 is the other
correct device):

Old:
sdb6: 592 sectors
sdd6: 264 sectors

New:
sdb6: 2048 sectors
sdd6: 2048 sectors

if i modify the source code of the mdadm, but don't know how to make it
to set differently based on the partition..

thanks in advance!
Csaba
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Re: convert raid10 to raid0

[Tóth Csaba]

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.

regards,
Csaba
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Re: convert raid10 to raid0

[Neil Brown]

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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Re: convert raid10 to raid0

[Tóth Csaba]

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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Re: convert raid10 to raid0

[Tóth Csaba]

2010.07.07. 21:29 keltezéssel, Tóth Csaba írta:
> Hey List,
> 
> [...]

my mdadm -E:

minerva ~ # mdadm -E /dev/sdc6
/dev/sdc6:
          Magic : a92b4efc
        Version : 1.1
    Feature Map : 0x0
     Array UUID : a73f5902:accc2488:aecfdc14:05a6e2f4
           Name : minerva:5  (local to host minerva)
  Creation Time : Thu Nov 26 14:50:07 2009
     Raid Level : raid10
   Raid Devices : 4

 Avail Dev Size : 1434619910 (684.08 GiB 734.53 GB)
     Array Size : 2869239808 (1368.16 GiB 1469.05 GB)
  Used Dev Size : 1434619904 (684.08 GiB 734.53 GB)
    Data Offset : 592 sectors
   Super Offset : 0 sectors
          State : clean
    Device UUID : a8f10e59:dbf96c47:4c4eb9bd:2db4c161

    Update Time : Wed Jul  7 10:34:32 2010
       Checksum : df7a8ba6 - correct
         Events : 0

         Layout : near=2
     Chunk Size : 512K

   Device Role : spare
   Array State : ...A ('A' == active, '.' == missing)

minerva ~ # mdadm -E /dev/sdd6
/dev/sdd6:
          Magic : a92b4efc
        Version : 1.1
    Feature Map : 0x0
     Array UUID : a73f5902:accc2488:aecfdc14:05a6e2f4
           Name : minerva:5  (local to host minerva)
  Creation Time : Thu Nov 26 14:50:07 2009
     Raid Level : raid10
   Raid Devices : 4

 Avail Dev Size : 1434620238 (684.08 GiB 734.53 GB)
     Array Size : 2869239808 (1368.16 GiB 1469.05 GB)
  Used Dev Size : 1434619904 (684.08 GiB 734.53 GB)
    Data Offset : 264 sectors
   Super Offset : 0 sectors
          State : clean
    Device UUID : 2536b63d:4cb4de23:1b8e3157:f4031701

    Update Time : Wed Jul  7 10:34:32 2010
       Checksum : d99dda94 - correct
         Events : 3981420

         Layout : near=2
     Chunk Size : 512K

   Device Role : Active device 3
   Array State : ...A ('A' == active, '.' == missing)


thanks in advance,
Csaba
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