I've found that, after using some btrfs filesystems for some time, that the first large write after a reboot takes a very long time. So I went to work trying out different test cases to simplify reproduction of the issue, and I've got it down to just these steps: 1) mkfs.btrfs on a large-ish device. I used a 14TB MD RAID5 device. 2) Fill it up a bit over half-way with ~5MB files. In my test I made 30 copies of a 266GB data set consisting of 52,356 files and 20,268 folders. 3) umount 4) mount 5) time fallocate -l 2G /mount/point/2G.dat real 3m9.412s user 0m0.002s sys 0m2.939s By comparison, if I don't use space cache things go much better: # umount # mount -o nospace_cache # time fallocate -l 2G /mount/point/2G.dat real 0m15.982s user 0m0.002s sys 0m0.103s If I use the clear_cache mount option, that also resolves the slowness. Is this a known issue? For me it's 100% reproducible, on various kernel versions including 3.14-rc8. Is there anything I should provide to help debug? -Justin -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
