From README.Debian in the bind9 package:
Any zones you are secondary for should be configured in
named.conf with simple filenames (relative to /var/cache/bind), so the data
files will be stored in BIND's working directory (defaults to /var/cache/bind).
Zones subject to automatic updates via DHCP should be stored in /var/lib/bind,
and specified with full pathnames.
If there are cases where you believe this is in error, I suggest discussing this with the bind9 maintainer.
From README.Debian in the bind9 package:
Any zones you are secondary for should be configured in
named.conf with simple filenames (relative to /var/cache/bind), so the data
files will be stored in BIND's working directory (defaults to /var/cache/bind).
Zones subject to automatic updates via DHCP should be stored in /var/lib/bind,
and specified with full pathnames.
If there are cases where you believe this is in error, I suggest discussing this with the bind9 maintainer.