installed centos7 on 4 colo servers, dual booting with pre-existing centos6.

the grub2 os-prober strategy is not very well thought out (and takes quite
a long time so i've removed execute permission from 30_os-prober.conf).
its primary weakness is its results are out of date every time the other OS
updates to a new kernel.

legacy-configfile is far more sensible, as it always boots the most recent
centos6 kernel.  (hello grub designers, configfile or legacy-configfile
should be the default approach, much more sensible than os-prober results
that get out of date!)  (and hello centos maintainers, centos7 has its own
grub2-mkconfig, it also would be more sensible for it to generate
configfile and/or legacy-configfile!)

on 3 out of the 4 centos7 installs, legacy-configfile works like a charm.
on the 4th, it gets "error: couldn't load file /vmlinuz-2.6.32-..."  (tho
entries in grub.cfg boot fine).

during 2 out of the 4 centos7 installs manual partitioning got something
like 'insufficient embedding space with filesystem type ext4' (hello
anaconda maintainers this message is misleading, it has nothing to do with
the partition type or filesystem type), and would not proceed until i
deleted the first existing partition, the centos6 boot partition.  before
deleting it i copied the contents to another partition (to be more exact
each server has 2 discs and each partition is setup as raid1 with identical
partitioning on the other disc, all setup utilizing the centos6&7
installers) and adjusted the grub.conf entries from root (hd0,1) to root
(hd0,2) to correspond to the new centos6 boot partition.  these entries
boot fine on one of these 2 servers, but the other box gives the above
error when attempting to boot any of the entries on the legacy-configfile
menu.  i've doublechecked the partition numbers (sd[ab]3) and root
commands.  no idea what to look for next.
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