Hi,
first - you have to understand what FastBack is and what it is not.
FastBack can replicate DISKS (partitions) between client and the server repository. It has no knowledge about application within the partition. As it uses VSS (on Windows), application as MSSQL, MS Exchange (and other with VSS writers) are in consistent state when the VSS snapshot is run.
I was told by FastBack instructor that for large (he was speaking about 100GB+) and heavily loaded applications the VSS writer is unable to flush all data to disk in time, so it can fail.
If you have an application without VSS support, you can use "pre/post backup scripts" to freeze/unfreeze the application to achieve consistent image to transfer.
Great thing on FastBack is that is is block-level incremental forever backup.
Starting with version 6.1 there is a support for Linux. There is no support for AIX in the roadmap (I've been told ...)
Harry