Ha! Interesting!
Their knowledge of lower level sys calls is way beyond mine, but it is curius that they have used a tar file for performance reasons.
Fwiw, the AntTP implementation of tarchive stores the self encrypted chunks (in a hybrid memory/disk LRU cache) for the tar file, rather than the tar file itself.
It is done this way to optimise the data retrieval from the autonomi network (much longer than any sys calls to disk). Perhaps similar goals in some way, but different extremes of optimisation.
Why only store the chunks? Well, the data remains encrypted up until the point it is served. This does improve security, as no data is stored decrypted on the host. However, it does the chunks required in the response must be decrypted each time.
So, I’ve mused over having a mode which stores the decrypted content in the cache. It would certainly speed up response times pretty massively (orders of magnitude, I suspect), but it does come at a security/privacy cost.
Edit: btw, there is potential to cache decrypted chunks in memory (until rotated out), which could balance the performance vs security element. Maybe something to consider.