From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: Fwd: mdadm format for manual destriping Date: Mon, 26 Oct 2015 15:13:15 -0400 Message-ID: <562E7B4B.2090800@turmel.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Marek , Linux-RAID List-Id: linux-raid.ids 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 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