Hi, On Wed, 4 May 2011 18:02:16 +0200, dexen deVries wrote: > Hi, > > a possibly naive question: how are files allocated on nilfs? > > Asking, because I've expected a large-ish (128MB) file to be mostly > continuous, modulo segment headers. But it doesn't seem so. A small test to > narrow down the question: > 0) created a new, empty, nilfs, on a separate partition (about 1GB size) > 1) created a file with dd if=/dev/zero of=a.bin bs=$((128*1024*1024)) count=1 > 2) ran hdparm --fibmap a.bin > output: > byte_offset begin_LBA end_LBA sectors > 0 231 16446 16216 > 8302592 16503 29094 12592 > 14749696 29239 32830 3592 > 16588800 32895 49214 16320 > 24944640 49255 58158 8904 > 29503488 58327 65598 7272 > 33226752 65663 81982 16320 > 41582592 82007 87230 5224 > 44257280 87415 98366 10952 > 49864704 98431 114750 16320 > 58220544 114759 116302 1544 > 59011072 116503 131134 14632 > 66502656 131191 145374 14184 > 73764864 145519 147518 2000 > 74788864 147583 163902 16320 > 83144704 163951 174446 10496 > 88518656 174607 180286 5680 > 91426816 180351 196670 16320 > 99782656 196703 203518 6816 > 103272448 203695 213054 9360 > 108064768 213119 229438 16320 > 116420608 229455 232590 3136 > 118026240 232783 245822 13040 > 124702720 245887 261662 15776 > > > while the first chunk of file fills almost whole segment, several subsequent > chunks are much smaller than segment. Why is it so? You can see what's happening easily by using 'dumpseg' tool. I guess it's because checkpoint is periodically created and some modified blocks of meta-data are inserted for the checkpoint creation. For your information, disk layout image of nilfs is found on the page 10 of the following slides: http://www.nilfs.org/papers/jls2009-nilfs.pdf Regards, Ryusuke Konishi -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
