Add unit-conversion-and-relative-sizing spec

Change-Id: I12c6c53f6e83fc4167942165a7015ed095b060e4

specs/size-unit-conversion-and-relative-sizing.rst

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+..
+
+This work is licensed under a Creative Commons Attribution 3.0 Unported License.
+http://creativecommons.org/licenses/by/3.0/legalcode
+
+
+========================================
+Size unit conversion and relative sizing
+========================================
+
+https://blueprints.launchpad.net/bareon/+spec/size-unit-conversion-and-relative-sizing
+
+Problem description
+===================
+
+The only size unit Bareon currently supports is MiB. Users often want to use
+both GiB and MiB, as well as relative sizes like 50%, which is impossible.
+
+Proposed change
+===============
+
+NOTE: This is a contribution of the feature developed within Cray OpenStack project.
+We will try to make a minimum changes to existing code.
+
+All “size” values are strings containing either an integer number and size
+unit (e.g., “100 MiB” or 100MiB”).
+
+Available measurement units are:
+
+    - ‘MB’, ‘GB’, ‘TB’, ‘PB’, ‘EB’, ‘ZB’, ‘YB’,
+    - ‘MiB’, ‘GiB’, ‘TiB’, ‘PiB’, ‘EiB’, ‘ZiB’, ‘YiB’
+
+Also relative values are supported for partition, pv and lv.
+Relative values use the size of the containing device or volume group as a
+base. For example, specifying “40%” for a 100MiB disk would result in a
+40MiB partition. Obviously, relative sizes cannot be used for disks.
+
+The user can also specify “remaining” as a size value for a volume in a disk
+or in a volume group. When “remaining” is specified, all remaining free space on
+the drive after allocations are made for all other volumes will be used for
+this volume.
+
+All the conversion is done in Ironic data driver, before the schema is mapped to
+object model. Internally we continue to use MiB everywhere.
+
+Alternatives
+------------
+
+None.
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+- max_lobur
+
+Milestones
+----------
+
+See blueprint ref above.
+
+Work Items
+----------
+
+- rebase on bareon master.
+
+Dependencies
+============
+
+None.