fragmention issue with ext4: e4defrag?

Hello,

Has anyone some experience using defragmentation tools on Linux against tablespaces ?

we are facing fragmentation problems with postgres instances having a few TB of data.
( RAID 5 )

I/O througput decreased from 300MB/s to 160.


- We first moved some schemas to separate servers.
  After that we still have  150'000 tables in 1.5 TB

- Now we are in the process of vacuuming FULL historical tables which are not written anymore.
  This seems to improve the I/O considerably

Our remaining issue is that the free space fragmentíon is still suboptimal
so that fragmention will probably start again soon.

Would it make sense to use a tool like e4defrag
(http://www.linux.org/threads/online-defragmentation.4121/)
in order to defrag the free space ?
And how safe is it to use such a tool against a running postgres instance?



many thanks,

Marc Mamin