Two kinds of mirrors exist: pre-mirrors and regular mirrors.
The
PREMIRRORS
and
MIRRORS
variables point to these, respectively.
BitBake checks pre-mirrors before looking upstream for any
source files.
Pre-mirrors are appropriate when you have a shared directory
that is not a directory defined by the
DL_DIR
variable.
A Pre-mirror typically points to a shared directory that is
local to your organization.
Regular mirrors can be any site across the Internet that is used as an alternative location for source code should the primary site not be functioning for some reason or another.