Ø  Flashbackup will improve the performance (it caches the data as a sort of snapshot then backs-up the snapshot so it's like a large file rather than loads of small ones, or something like that....) but because it works per volume, you need the space for the cache, which is at least the same size as the volume you are backing-up.

What FlashBackup really does is snapshot the volume and then do a *physical* backup of the volume – in other words, block by block, rather than walking the file system.  For file systems with lots of files, this can be a huge savings – we typically see FlashBackups complete in half the time that regular backups do.

The cache volume only needs to be as large as necessary to cache the writes to the volume while it was being backed up.  Unless you are in a very intensive write mode, this volume does not need to be as large as the volume being backed up – in fact, I’ve backed up in excess of 10TB of data with a shared cache volume of under 100GB and it was not getting close to filling (several GB would have sufficed).  The FlashBackup documentation explains how to size the cache volume.

The performance gain for FlashBackup depends on the overhead of your file system operations.  For NTFS, the overhead is quite high (but our big file systems are in the millions of files).  Additionally, NTFS is not very efficient in walking the file system in terms of allocating resources.  We find that FlashBackup is much more polite to the target than a traditional client backup.

   …/Ed