Hello, I have created a 500GB partition on my HDD and formatted it for btrfs. I created a file on it. # echo "tmp data in the tmp file.." > /mnt/btrfs/tmp-file # umount /mnt/btrfs
Next I want to know the blocks allocated for the file and I used filefrag for it. I get some information as follows - # mount -o max_inline=0 /dev/sdc2 /mnt/btrfs # filefrag -v /mnt/btrfs/tmp-file Filesystem type is: 9123683e File size of /mnt/btrfs/tmp-file is 27 (1 block, blocksize 4096) ext logical physical expected length flags 0 0 65924123 1 eof /mnt/btrfs/tmp-file: 1 extent found Now, I want to read the same data from the disk directly. I tried the following - block 65924123 = byte (65924123*4096) = 270025207808 # dd if=/dev/sdc2 of=tmp-file skip=270025207808 bs=1 count=4096 # cat tmp-file I cannot read the file's contents but some garbage. I read somewhere that the physical block number shown in filefrag may actually be a logical block for the file system and it has an additional translation to physical block number. So next I tried the following - # btrfs-map-logical -l 65924123 /dev/sdc2 mirror 1 logical 65924123 physical 74312731 device /dev/sdc2 mirror 2 logical 65924123 physical 1148054555 device /dev/sdc2 I again tried reading the block 74312731 using the dd command as above, but it is still not the right block. I want to know what does the physical block number returned by filefrag mean, why there are two mappings for the above block number and how I can find the exact physical disk block number the file system actually writes to. My sdc has the following partitions: Device Boot Start End Blocks Id System /dev/sdc1 2048 419432447 209715200 83 Linux /dev/sdc2 1468008448 2516584447 524288000 83 Linux (BTRFS) /dev/sdc3 419432448 1468008447 524288000 83 Linux Thanks, Aastha. -- 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
