On 2015-11-12 13:47, Austin S Hemmelgarn wrote: >> That's a pretty unusual setup, so I'm not surprised there's no quick and >> easy answer. The best solution in my opinion would be to shuffle your >> partitions around and combine sda3 and sda8 into a single partition. >> There's generally no reason to present btrfs with two different >> partitions on the same disk. >> >> If there's something that prevents you from doing that, you may be able >> to use RAID10 or RAID6 somehow. I'm not really sure, though, so I'll >> defer to others on the list for implementation details. > RAID10 has the same issue. Assume you have 1 block. This gets stored > as 2 copies, each with 2 stripes, with the stripes split symmetrically. > For this, call the first half of the first copy 1a, the second half 1b, > and likewise for 2a and 2b with the second copy. 1a and 2a have > identical contents, and 1b and 2b have identical contents. It is fully > possible that you will end up with this block striped such that 1a and > 2a are on one disk, and 1b and 2b on the other. Based on this, losing > one disk would mean losing half the block, which would mean based on how > BTRFS works that you would lose the whole block (because neither copy > would be complete).
Does it equally apply to RAID1? Namely, if I create mkfs.btrfs -mraid1 -draid1 /dev/sda3 /dev/sda8 then btrfs will "believe" that these are different drives and mistakenly think that RAID pre-condition is satisfied. Am I right? If so then I think this is a trap, and mkfs.btrfs should at least warn (or require --force) if two partitions are on the same drive for raid1/raid5/raid10. In other words, the only scenario when this check should be skipped is: mkfs.btrfs -mraid0 -draid0 /dev/sda3 /dev/sda8 -- With best regards, Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
