On 2017-02-03 11:44, Lakshmipathi.G wrote: > Hi. > > Came across this thread https://www.mail-archive.com/linux-btrfs@xxxxxxxxxxxxxxx/msg55161.html > Exploring possibility of adding test-scripts around these area using dump-tree & corrupt-block.But > unable to figure-out how to get parity of file or find its location. dump-tree output gave, > > item 5 key (FIRST_CHUNK_TREE CHUNK_ITEM 145096704) itemoff 15557 itemsize 144 > length 134217728 owner 2 stripe_len 65536 type DATA|RAID5 > io_align 65536 io_width 65536 sector_size 4096 > num_stripes 3 sub_stripes 0 > stripe 0 devid 3 offset 63111168 # Is this parity?Seems empty? > dev_uuid f62df114-186c-4e48-8152-9ed15aa078b4 > stripe 1 devid 2 offset 63111168 # Contains file data-stripe-1 > dev_uuid c0aeaab0-e57e-4f7a-9356-db1878876d9f > stripe 2 devid 1 offset 83034112 # Contains file data-stripe-2 > dev_uuid 637b3666-9d8f-4ec4-9969-53b0b933b9b1 > thanks. IIRC, the parity is spread across the disk stripes of the chunk. So first you have to find the logical-offset [LO] where the the file begins. Then you have to map this offset to the chunk which holds the data. The chunk has the following info: - chunk start [CS], chunk length [CL] - for each stripe: where the stripe starts If you subtract the chunk-start from the logical-offset [ CO == LO-CS], you will find the offset where the data belongs in the chunk. As stated above, the PARITY is spread across the chunk stripes. So (supposing that the stripe size is 64K, the raid level is 5, the disks are three), - the first 64k of stripe 0, is data [0..64K) - the first 64k of stripe 1, is data [64..128K) - the first 64k of stripe 2 is parity, - the 2nd 64k of stripe 0 is parity, - the 2nd 64k of stripe 1, is data [128..196K) - the 2nd 64k of stripe 2, is data [192..256K) - the 3rd 64k of stripe 0, is data [256..320K) - the 3rd 64k of stripe 1 is parity, - the 3rd 64k of stripe 2, is data [320..384K) and so on, To find the data, You have to compare the CO to the data [...) range. If you look to an my old patch (unfinished :-( ), you can find some example to dump the different stripe [BTRFS-PROGS][PATCH][V2] Add two new commands: 'btrfs insp physical-find' and 'btrfs insp physical-dump' > Cheers. > Lakshmipathi.G > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it> Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
