There's plenty of threads on here about Defrag for Ext3 and Ext4 and largely it seems E4Defrag is the most reliable new way to defrag in Linux.
But, there is no mention of whether e4defrag is backward compatible with Ext3 and can support / optimize it? e3defrag(8)
If not, what is the reliable stable method today in 2017?
(Most of the previous threads are dated 2010/ 11 and that is half a decade in fast moving tech time frames)
PS: Yes, it is not always needed as it says here, But, I'd like to defrag a fragmented volume before I archive it.
PPS: Cant convert this to ext4 as older systems that only support ext3 need to access it.