Next-generation Linux file systems: NiLFS(2) and exofs (developerWorks)

1 - At a guess, this may happen, although depending on how it's implemented, the effects may be reduced by delayed allocation & writeback, which can lump together writes to occur all at the same time and contiguously, rather than as they happen which would interleave the files.

2 - you don't write over stuff that's still in use, but usually set a data retention policy to say how long to keep snapshots for (or what resolution of snapshots to keep - eg, every week take a snapshot that will keep for a year, but all other snapshots taking during the week can be overwritten after 2 weeks). If you need to write something to disk but all of the space is covered by current data or snapshots, then you'd simply get an out of disk space error as you would with any other filesystem, so it's not wise to set an overly optimistic data retention policy.