2017-04-25 13:08 GMT+02:00, Andreas Klauer <Andreas.Klauer@xxxxxxxxxxxxxx>: > On Tue, Apr 25, 2017 at 12:40:37PM +0200, Patrik Dahlström wrote: >> I was thinking if it was in fact a 5 disk raid + garbage from 1 disk, >> then the checksum would be correct if the garbage disk was filtered >> out. Does that make sens? > > No. With one disk missing there is no parity (no way to verify it). > >> You mentioned something about linear device mapping before. What is >> that? Is it something I could experiment with? How do I do that? > > https://www.kernel.org/doc/Documentation/device-mapper/linear.txt > > Once you have found where data overlaps on both raids, you create > a linear mapping of start..X of the 6disk raid, followed by X..end > of the 5disk RAID. > > That way you get a device that holds your data intact as a whole, > whereas the raid sets would give you the first half of data on > the 6disk raid set (what was already reshaped) and the other half > on the 5disk raid set (what had yet to be reshaped). > > This is only a way to get read access at the data, making the raid > work as a standalone again (resume reshape with lost raid metadata) > is another problem, to be tackled after you backed up your data ;) I'm not sure how I would backup 20 TB of data. I'll backup what I can, of course. The most essential. > >> Output of examine calls: > >> /dev/mapper/sda: >> Data Offset : 252928 sectors > >> /dev/mapper/sda-2: >> Data Offset : 252928 sectors > > Wrong. > > mdadm --grow changes the offset, so: Oh, I see. Does it do that every time I grow? In that case the original 5disk raid won't have 128M offset either. The full history of this raid: 1. 2x6 TB + md0 (4x2 TB striped) <- data offset at 128M 2. replace md0 with 6 TB, rebuild data. Shouldn't change data offset since this is basically the same as replacing a faulty disk, right? 3. Grow to 4x6 TB <- data offset changed (unknown). 4. Grow to 5x6 TB <- data offset changed (unknown). 5. Grow to 6x6 TB <- data offset changed. This is when the problem started. Does the data offset change by a fixed or calculated value? Can I calculate the data offset by comparing to known data? I must say that you help has been most valuable. You have my eternal gratitude. Best regards // Patrik -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
