Hi Marek,

{ Top-posting fixed.  Please don't do that. }

On 10/26/2015 02:09 PM, Marek wrote:

On Saturday, October 24, 2015, Marek [off-list ref] wrote:

quoted

is there a documentation available on how mdadm stores data? E.g.

Yes, the man pages.  Try "man md" and "man mdadm" in a console.  This
documentation is provide by the kernel team and, other than the source
code itself, is expected to be definitive.

quoted

1.  super-block

The location of the superblock is described in "man md".  The precise
content of the superblock is only detailed in the source code.

quoted

2.  offset of first block on each drive

Zero for metadata versions 0.90 and 1.0.  Configurable for metadata
versions 1.1 and 1.2.  See the --data-offset option in "man mdadm".

quoted

3. whether mdadm stores blocks as raw data or stores some kind of
metadata associated with each block e.g. disk 1 -> data_block1
immidiatelly followed by data_block 5 or
metadata_for_block_1 | data_block 1 |  metadata_for_block_5 | data_block 5 |

No metadata per block.

quoted

4. how and where mdadm stores its backup superblock

None, although each device has one.

quoted

5. what klind of XOR algorithm is used by mdadm

Straight parity for raid4, raid5, and the 'P' blocks of raid6.  Galois
field arithmetic for the 'Q' blocks of raid6.

https://www.kernel.org/pub/linux/kernel/people/hpa/raid6.pdf

[trim /]

Does the first block start immediately after 258 bytes?

No.

Also question 3,4,5

See above and in the man pages.

HTH,

Phil