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I'm switching my Windows server to Ubuntu and am trying to get my software RAID1 (mirror) that I created in Windows to show up in Ubuntu. I have read that this is possible here using mdadm, but I'm having trouble.

Here is what I'm trying:

Script started on Thu 12 Jan 2012 12:22:33 GMT
graeme@MediaCentre:~/Desktop$ cat /proc/partitions

major minor  #blocks  name

   8        0  120060864 sda
   8        1  117974016 sda1
   8        2          1 sda2
   8        5    2083840 sda5
   8       16 1465138584 sdb
   8       17 1465136128 sdb1
   8       32 1465138584 sdc
   8       33 1465136128 sdc1
graeme@MediaCentre:~/Desktop$ sudo mdadm --build /dev/md0 --chunk=128 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
[sudo] password for graeme:
mdadm: array /dev/md0 built and started.
graeme@MediaCentre:~/Desktop$ sudo mkdir /media/WinMirror/
mkdir: cannot create directory `/media/WinMirror/': File exists
graeme@MediaCentre:~/Desktop$ sudo mount -t ntfs /dev/md0 /media/WinMirror
Failed to read last sector (5860544511): Invalid argument
HINTS: Either the volume is a RAID/LDM but it wasn't setup yet,
   or it was not setup correctly (e.g. by not using mdadm --build ...),
   or a wrong device is tried to be mounted,
   or the partition table is corrupt (partition is smaller than NTFS),
   or the NTFS boot sector is corrupt (NTFS size is not valid).
Failed to mount '/dev/md0': Invalid argument
The device '/dev/md0' doesn't seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?
graeme@MediaCentre:~/Desktop$ exit
exit

Script done on Thu 12 Jan 2012 12:23:23 GMT

I get the same thing when I try 64 chunks, and if I list the disks in the other order.

Does anyone know what I'm doing wrong here?

Edit: I'm adding the results of fdisk -l as requested by Paul:

graeme@MediaCentre:~$ sudo fdisk -l /dev/sdb
[sudo] password for graeme:

Disk /dev/sdb: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x181bfef8

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1              63  2930275119  1465137528+  42  SFS
graeme@MediaCentre:~$ sudo fdisk -l /dev/sdc

Disk /dev/sdc: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x181bfef8

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1              63  2930275119  1465137528+  42  SFS
graeme@MediaCentre:~$ sudo mdadm --build /dev/md0 --level=1 --raid-devices=2 /dev/sdb     /dev/sdc
mdadm: array /dev/md0 built and started.
graeme@MediaCentre:~$ sudo fdisk -l /dev/md0

Disk /dev/md0: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x181bfef8

    Device Boot      Start         End      Blocks   Id  System
/dev/md0p1              63  2930275119  1465137528+  42  SFS
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What does sudo fdisk -l /dev/md0 give you? –  Paul Jan 12 '12 at 22:39
    
I've edited the original post to add the fdisk -l output. I guess becuase it's showing as ID 42 because it's a "dynamic disk" that doesn't use the normal partition table (I have read it uses 1MB at the end of the disk for the partition table). Perhaps I just need to find a way of mounting a dynamic disk? –  Grezzo Jan 13 '12 at 9:44
    
Is LDM a possible solution to this? I have no idea how to get it working with LDM yet –  Grezzo Jan 13 '12 at 9:53
1  
This similar question has a positive answer stackoverflow.com/questions/8427372/… –  Costin Gușă Mar 12 '13 at 21:32
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4 Answers

up vote 1 down vote accepted

I'm pretty sure it can't be done. I tried everything to no avail, and eventually realised I'd buggered it do that windows wouldn't even mount it any more. Had to use some advanced recovery tools. Massive blunder! Feel like a right idiot relying on raid with no backup an messing with the raid with no backup! Oh well. Lesson learned.

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I think I've just discovered that it's not possible to "build" a RAID1 and "build"ing is the only way to view a Windows software RAID. Can someone confirm that for me?

This is what I managed to get out of mdadm:

graeme@MediaCentre:~$ sudo mdadm --build --help
Usage:  mdadm --build device -chunk=X --level=Y --raid-devices=Z devices

 This usage is similar to --create.  The difference is that it creates
 a legacy array without a superblock.  With these arrays there is no
 difference between initially creating the array and subsequently
 assembling the array, except that hopefully there is useful data
 there in the second case.

 The level may only be 0, raid0, or linear.
 All devices must be listed and the array will be started once complete.
 Options that are valid with --build (-B) are:
  --bitmap=          : file to store/find bitmap information in.
  --chunk=      -c   : chunk size of kibibytes
  --rounding=        : rounding factor for linear array (==chunk size)
  --level=      -l   : 0, raid0, or linear
  --raid-devices= -n : number of active devices in array
  --bitmap-chunk=    : bitmap chunksize in Kilobytes.
  --delay=      -d   : bitmap update delay in seconds.
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This:

sudo mount -t ntfs /dev/md0 /media/WinMirror

attempts to mount the raid array as a whole, whereas the fdisk shows you have it partitioned:

    Device Boot      Start         End      Blocks   Id  System
/dev/md0p1              63  2930275119  1465137528+  42  SFS

To mount the partition, you should use:

sudo mount -t ntfs /dev/md0p1 /media/WinMirror
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This still doesn't work because it doesn't think it is an ntfs formatted partition. Failed to read last sector (5860544511): Invalid argument [...] HINTS: Either the volume is a RAID/LDM but it wasn't setup yet, or [...] The device '/dev/md0p1' doesn't seem to have a valid NTFS. ID 42 means that it is a windows dynamic disk (LDM) with a separate partition table at the end. I think mount cannot read the LDM partion within "ID 42" partition. Does this sound possible? –  Grezzo Jan 13 '12 at 15:22
    
@Grezzo Ah, sorry yes. I don't think you can mount LDM under linux. You may need to use Windows to convert it to a non-dynamic drive first. –  Paul Jan 13 '12 at 22:36
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I can totally confirm that you can do it with mdadm, and a few simple commands:

mdadm --build /dev/md0 --level=0 --raid-devices=2 /dev/sdc1 /dev/sdb1
mount /dev/md0 /mount/raid

More Details:

  • You have to install mdadm first of course (terminal command: sudo apt-get install mdadm).
  • "md0" is just the name I gave to the raid, for use in Linux; you can call it whatever.
  • the "--level=0" part most likely refers to the kind of RAID, in my case RAID 0.
  • the "--raid-devices=2" part most likely is the number of HDDs in the RAID.
  • You have to first create the folder "/mount/raid" (or wherever you want to mount it or call it)
  • In my case I had a software RAID 0 made in windows 7/8, on two 2TB HDDs (here sdc1 and sdb1). Here, sdc1 is put first in the command because it contained the RAID info; if you receive some error saying that there's no RAID info, you can try switching between them and you should be OK.

CAUTION: don't use mdadm --create command if you already have the software RAID made in Windows, as I THINK it might overwrite the RAID info, and you'll end up ducking your raid and the data on it.

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In the first section of my question it shows that I tried those two commands, but they don't work. Probably because I had a RAID0, not a RAID1 like you –  Grezzo Aug 1 '13 at 13:59
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