Just a little update: Nonetheless my issues with fallocate and the bigalloc'ed fs, I tried to dd a couple of ISOs on the key and check whether I could boot from them. And to my great surprise... The answer was yes. $ ls -l /run/media/neitsab/iso/_ISO/ total 4980736 drwxr-xr-x 2 neitsab users 4096 17 avril 21:38 . drwxr-xr-x 4 neitsab users 4096 17 avril 19:36 .. -rw------- 1 neitsab users 964689920 17 avril 21:37 gnome-3.12.iso -rw------- 1 neitsab users 1589166080 17 avril 20:45 manjaro-gnome-0.8.9-x86_64.iso -rw------- 1 neitsab users 993001472 17 avril 21:38 openSUSE-13.1-GNOME-Live-x86_64.iso I can boot from the two others but not from manjaro's one, which happens to be the biggest too. A comparison of xfs_io output : $ xfs_io -f -c "fiemap -v" '/run/media/neitsab/iso/_ISO/manjaro-gnome-0.8.9-x86_64.iso' /run/media/neitsab/iso/_ISO/manjaro-gnome-0.8.9-x86_64.iso: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..262143]: 3145728..3407871 262144 0x0 1: [262144..524287]: 3407872..3670015 262144 0x0 2: [524288..786431]: 3670016..3932159 262144 0x0 3: [786432..1048575]: 3932160..4194303 262144 0x0 4: [1048576..1310719]: 4194304..4456447 262144 0x0 5: [1310720..1572863]: 4456448..4718591 262144 0x0 6: [1572864..1835007]: 5242880..5505023 262144 0x0 7: [1835008..2097151]: 5505024..5767167 262144 0x0 8: [2097152..2359295]: 5767168..6029311 262144 0x0 9: [2359296..2621439]: 6029312..6291455 262144 0x0 10: [2621440..2883583]: 6291456..6553599 262144 0x0 11: [2883584..3103839]: 6553600..6773855 220256 0x1 $ xfs_io -f -c "fiemap -v" '/run/media/neitsab/iso/_ISO/openSUSE-13.1-GNOME-Live-x86_64.iso' /run/media/neitsab/iso/_ISO/openSUSE-13.1-GNOME-Live-x86_64.iso: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..262143]: 8912896..9175039 262144 0x0 1: [262144..524287]: 9175040..9437183 262144 0x0 2: [524288..786431]: 9437184..9699327 262144 0x0 3: [786432..1048575]: 9699328..9961471 262144 0x0 4: [1048576..1310719]: 9961472..10223615 262144 0x0 5: [1310720..1572863]: 10223616..10485759 262144 0x0 6: [1572864..1835007]: 10485760..10747903 262144 0x0 7: [1835008..1939455]: 10747904..10852351 104448 0x1 $ xfs_io -f -c "fiemap -v" '/run/media/neitsab/iso/_ISO/gnome-3.12.iso' /run/media/neitsab/iso/_ISO/gnome-3.12.iso: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..262143]: 6815744..7077887 262144 0x0 1: [262144..524287]: 7077888..7340031 262144 0x0 2: [524288..786431]: 7340032..7602175 262144 0x0 3: [786432..1048575]: 7602176..7864319 262144 0x0 4: [1048576..1310719]: 7864320..8126463 262144 0x0 5: [1310720..1572863]: 8126464..8388607 262144 0x0 6: [1572864..1835007]: 8388608..8650751 262144 0x0 7: [1835008..1884159]: 8650752..8699903 49152 0x1 So they're all contiguous but Manjaro. I guess that brings us back to the randomness of block allocation as explained by Lukáš and to an effect of file size on the probability to be non-contiguous (which is rather logical)! Thanks all for your explanations, Cheers -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
