All non-head block_log parts should be by default opened as read only, if they have matching artifact files
This would allow to share most of block_log contents across few nodes started on single host (due to trivial symlinking to common location). Of course all parts built from incoming blocks will be duplicated still, but since every part contains c.a. 1 month of blockchain lifetime it can be adjusted by regular administration tasks specific to given node.
We can also consider opening any block log in read only mode (also only if artifact files match) when --stop-at-block
is specified (and block is covered by given block log).