SD cards query

There are probably a bunch of different approaches none of which are individually bullet proof so, you should always have a second copy somewhere else to mitigate against the risk of loss.

This in itself causes issues of synchronisation of the sources etc...

A SD is fine. Like anything it will have a mean time between failure, expected number of write cycles, etc, but mostly now a quality card will last what would be expected a normal life span for such a device.

If bandwidth isn't a problem (and privacy ala NSA implications etc.) then give free online storeage a blast (dropbox, box, google drive,microsoft's skydrive or whatever its equivalent name is now) as a second and backup copy. Or you could do the online thing twice with no SD - Dropbox and Box for example, and not use SD at all. Have one online as your primary and second as a backup.

As I said there are many ways of skinning this particular cat, but more important in my mind is having security of a second backup somewhere (and this may be more troublesome - in terms of keeping in sync etc..).