I'm running a synology nas DS1817+ with DSM 6.2.2-24922 with a RAID5 volume formatted with BTRFS.
Deleting a large file either with DSM FileStation or directly in an ssh session with "rm filename" takes a long time.
bash-4.3# ls -al
total 31362720
drwxr-xr-x 1 root root 154 Apr 13 05:09 .
drwxr-xr-x 1 root root 86 Apr 13 05:09 ..
-rw------- 1 root root 42949672960 Apr 13 05:09 Zoll-VM-flat.vmdk
bash-4.3# time rm Zoll-VM-flat.vmdk
real 7m24.817s
user 0m0.000s
sys 0m6.435s
Why? Looking at iotop it seems to be, that it reads and writes the whole file?!?