Most of the documentation is a snapshot of the old Namesys site (archive.org, 2007-09-29).
There was also a Reiser4 Wiki (archive.org, 2007-07-06) once on pub.namesys.com.
Reiser4 development appears to have stalled and ReiserFS is deprecated and scheduled to be removed from mainline Linux in 2025.
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From Reiser4 FS Wiki
- ...l server gets its batteries disconnected accidentally by the UPS company's service crew, or your kernel was not as ready for prime time as you hoped, or the s ... own block. We don't have fixed space allocation for inodes. That saves 6% of your disk.81 KB (13,616 words) - 11:47, 21 December 2010