On Sun, Oct 31, 2010 at 11:12:41AM +0100, Alex Bligh wrote: > I want to generate or extend a large file in an ext4 filesystem allocating > space (i.e. not creating a sparse file) but not actually writing any data. Well, some metadata will have to be written, but not data. shouldn't posix_fallocate(3) and/or fallocate(2) do that? I haven't got EXT4 around ATM, but IIRC it should work on it too. On XFS it seems to work too: # time fallocate -l 3000000000 /stuff/tmp/bla fallocate -l 3000000000 /stuff/tmp/bla 0,00s user 0,00s system 0% cpu 0,402 total # du -h /stuff/tmp/bla 2,8G /stuff/tmp/bla # du -bh /stuff/tmp/bla 2,8G /stuff/tmp/bla # rm -f /stuff/tmp/bla fallocate(1) is from util-linux on my Debian Squeeze Oppose that to dramatically slower dd(1), which fills them with zeros explicitely: # time dd if=/dev/zero of=/stuff/tmp/bla count=30000 bs=100000 time dd if=/dev/zero of=/stuff/tmp/bla count=30000 bs=100000 30000+0 records in 30000+0 records out 3000000000 bytes (3,0 GB) copied, 31,2581 s, 96,0 MB/s dd if=/dev/zero of=/stuff/tmp/bla count=30000 bs=100000 0,00s user 3,41s system 10% cpu 31,341 total # du -h /stuff/tmp/bla 2,8G /stuff/tmp/bla -- Opinions above are GNU-copylefted. _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
