Partition is not accessible in WinXP after being used in RAID 1 under Ubuntu

Question

I have created a RAID 1 array under Ubuntu using mdadm. I used the manual at this link: https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-16-04

I created a RAID 1 array using two partitions (on different hard drives). I selected the NTFS file system in order to read the data under Windows later. So after I created the RAID 1 array, I wrote a file on the md0 device and loaded Windows XP to check that this file will be on both partitions. But I was not able to open partitions under Windows XP. Windows XP assigned a drive letter to both partitions but when I try to open them it says:

file system is not available.

Is it possible to have two partitions under NTFS in RAID 1 on Ubuntu so that it could be possible to access them from Windows?

[UPDATE] Sorry for not giving a detailed information. I have two drives. I have created an ntfs partitions on both. Then under Ubuntu i used mdadm to combine them into raid 1 array. I wrote a file into md0. Then i have booted Windows XP from a third drive. Not a VM. I see that two partitions have a drive letter. One for each. But i can't see my file in them. I expect it to bee on both partitions. The first partition is not empty (i see it from disk properties) but when i open it there is no file. Another partition is shown as empty and can't be opened.

I was expecting that linux mdadm works in a way that it just mirrors the file write to both paritions so that they can be read from any other operating system later.

[quote] Windows doesn't understand mdadm natively (nitpicking: neither does Linux considering mdadm has to be installed) hence Windows sees the 2 drives (and partitions) as independent so it attributes "letters" but can't read the contents obviously. [/quote]

ChanganAuto why can't file can't be read separately from any partition from raid 1 array? [/UPDATE]

Answer 1

Is it possible to have two partitions under NTFS in RAID 1 on Ubuntu so that it could be possible to access them from Windows?

Yes, that is possible by making them available as network shares. This is an access on file level which allows you to create and delete files and folders. It is not a bare metal access which allows you to read and write specific sectors over the network. By using network shares, it does not matter for your XP client on which type of file system your linux host is managing your files.

As ChanganAuto underlined in his commentary this solution is not possible in a dual-boot environment because you would need to have two running operating systems. Maybe assiging two disks to a linux running in a virtual machine on a Windows host could solve the problem.

I was expecting that linux mdadm works in a way that it just mirrors the file write to both paritions so that they can be read from any other operating system later.

That is wrong. mdadm probably (I never used it) initialised your partition with a mdadm-specific header which has overwritten your file system metadata such as the boot sector and others. That initialisation deleted the NTFS boot sector. Probably mdadm wrote a summary file describing your mdadm setup somewhere in the linux directory tree.

As XP does not understand the mdadm header it fails to recognize the mdadm-structure. Furthermore where should XP get that summary information/configuration file from when it's only residing somewhere in your linux operating system partition directory tree?

You did not specify if you are using XP 32-bit or 64-bit. Assuming a typical sector size of 512 byte at the interface XP 32-bit can only address a maximum space of 2 TB using the outdated MBR partition table format instead of the modern GPT partition table format.

If you were using disks bigger than 2 TB you would have ran into a problem as you would have partitioned them with GPT on linux wich XP 32-bit does not understand.