I was doing a little seekwatchering today, and found something... interesting. I was doing an 8G buffered write via dd, on a machine that reports 3G of memory, in 1M chunks like so: dd if=/dev/zero of=/mnt/test/foobar bs=1024k count=8192 on a fairly decent hardware raid, ~90G filesystem. Kernel is 2.6.24-rc1, with all the git patches from a day or so ago applied. I made the ext4 fs with lustre's e2fsprogs, with -I 256, and mounted with: mount -t ext4dev -o data=writeback,delalloc,extents,mballoc /dev/sdb7 /mnt/test The resulting file had over 4k extents. [root@bear-05 ~]# filefrag -v /mnt/test/foobar | grep -i extents File is stored in extents format /mnt/test/foobar: 4075 extents found http://people.redhat.com/esandeen/seekwatcher/ext4-dd-write.png if I don't mount with delalloc: mount -t ext4dev -o data=writeback,extents,mballoc /dev/sdb7 /mnt/test and run the same dd, I get 229 extents: [root@bear-05 ~]# filefrag -v /mnt/test/foobar | grep -i extents File is stored in extents format /mnt/test/foobar: 229 extents found http://people.redhat.com/esandeen/seekwatcher/ext4-dd-write-nodelalloc.png It looks like delalloc is dribbling all over the disk.... (note: times & rates look wrong to me, something is up with blktrace I think, but FIBMAP shouldn't lie about allocation) -Eric - 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
