Updating from OS X to Yosemite on Macbook air seems to work OK if you have one Mac partition and one Windows/Bootcamp partition. But ...
If you have two windows partitions then the update will cause problems, the new partition setup created by Yosemite update was:
- One very small partition (~ < 200MB), probably booting data
- One Mac partition
- One Mac recovery tools partition (~600MB)
- One Bootcamp/windows partition
The MBR has space for 4 partitions (?!); so if you had two windows partitions, the second one (Fat32) might not be visible. In my case Mac could still see it and browse files, but windows 7 seen it as unpartitioned space.
I booted with an USB stick (Minitool Partition wizard free), deleted Mac "recovery" partition (to make room on MBR), created that 2nd windows partition from scratch. Did that without changing starting point of Bootcamp partition, otherwise windows might not boot.
You are losing the ability to boot into Mac recovery tools. But in worst case scenario you can delete all partitions and boot from network to re-install Mac from scratch.
I couldn't find a better solution to have two Windows partitions, tried re-installing and re-partitioning around 6 times, windows would fail to boot whenever I touched the bootcamp partition.
The tool should also work to re-size the bootcamp patition, as long as starting point remains unchanged.