Sahara destroys boot code on images of some architectures using each unmounted partition for HDFS

[Andrey Bubyr]

Sahara tries to detect all non-used (e.g. present, but unmounted) disk partitions, format them to XFS filesystem and use as HDFS volumes. This behaviour is destcructive, f.e. in case of IBM PowerPC architecture which requires small few-megabyte partition to boot (so-called IBM PReP partirion with partition type 41). Such assumption firstly, f.e. brakes Ambari cluster deployment, as few MB HDFS partition is not enough for normal function, and, secondary, completely ruins boot code (as partition is re-formatted by Sahara), and machine cannot be booted anymore

For my particular case I've created this workaround patch to sahara/service/volumes.py (simply checks if parition is IBM PReP and deletes it from allowed for Sahara usage):
http://paste.openstack.org/raw/595054/
https://github.com/abubyr/fuel-ppc64el/blob/master/sahara-patches/sahara-ignore-prep-part.patch

But anyway, I suggest to completely re-think the logic of detecting paritions for HDFS. It is not a good choice, on my opinion, to grab first unmounted disk without any checks (e.g. parition type, parition size as in current situation)