There is a *lot* of mis-information about raids out there!
Myth: After replacing a failed disk, the RAID array, will automatically re-build
Nothing could be further from the truth! A failed array must be manually re-built by the system administrator - the process once begun is largely automatic. Why the human intervention? Lets say someone wants to steal my data - if the array automatically rebuilt itself, all they would need to do is walk in with 3 drives and some time . . . There are RAID solutions involving a 4th "hot spare" - typically higher end SCSI controllers with battery backed up cache . .
I don't think countering misinformation with misinformation is a good idea.
A fair amount of RAID controllers have a feature called "auto rebuild", which is used to automatically rebuild arrays.
This is a perfectly normal feature in controllers supporting RAID 5, almost mandatory.
Cheaper and/or older controllers require a hot spare for rebuilding the array, more advanced and/or recent controllers can perform a bit more advanced action:
The Auto Rebuild policy determines how the controller firmware will attempt
to rebuild degraded units.
When Auto Rebuild is disabled, only spares will be automatically used to
rebuild degraded units. When Auto Rebuild is enabled, the firmware will
select drives to use for automatically rebuilding a degraded unit using the
following priority order.
• Smallest usable spare.
• Smallest usable unconfigured (available) drive.
• Smallest usable failed drive.
Enabling Auto Rebuild allows you to add a drive to the controller and have it
be available for a rebuild, without having to specify it as a spare.
With Auto Rebuild enabled, if you accidentally disconnect a drive (causing
the controller to see it as a failed drive) and then reconnect it, the controller
will automatically try to use it again.
You can enable or disable the Auto-Rebuild policy through 3DM or 3BM.
You will note that the 3ware controllers are not SCSI controllers, but SATA and PATA controllers.
And if someone has physical access to your drives in the first place, you're screwed in terms of data security, unless the volume or data is securely encrypted, regardless of whether it's possible to rebuild a RAID or not; RAID auto-rebuild or not is mostly irrelevant for that problem area.