Please keep in mind that Linux file system are constructed in such a way that defragmentation is not needed ( the kernel takes care about it ).
The fragmentation is on the level of about 1-2 %. Preparing an defragmentation algorithm is possible but not needed - the gain of performance will rather not be visible

Also the DSS does not understand the underlying file system on the LUN. With DSS, the disk is carved into Logical Volumes which are served to your servers. So no tools are provided to do any defragmentation.

If you are using iSCSI, then you can defragment your volumes by the operating system that host your iSCSI volumes, for example Windows O.S. as you can use it's defragmentation tool in case you used iSCSI.