Submitted by: @ibaseru

Interesting, but gbak have only option -use_all_space for restore, but does not have reverse option, to turn database flag no_reserve off.
gfix, instead, have -use full/reserve.
Thus, if I have backup, I can't turn no_reserve off.
I need to
- have existing database (or restore it from backup)
- run gfix -use reserve
- gbak -b
- gbak -c

which is a bit long way.

for the name of the option I can suggest -use_reserve, but it will conflict with -use_all..., because "default" part of the option is -use_
But, making it not default, I think, will not break any "existing functionality or scripts". Can vote for any other name of this option.