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 <mlf.conv@xxxxxxxxx> wrote:
>> 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.
>> 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.
>> 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".
>> 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.
>> 4. how and where mdadm stores its backup superblock
None, although each device has one.
>> 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
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