[PLUG] Disallow raid assembly with missing device?

[Aaron Ten Clay]

I've got a non-critical box running raid5 where two drives are external, one 
USB and one eSATA. Occasionally for some reason one or the other is not 
detected at boot time, and the kernel will autodetect and assemble the array 
in degraded state missing one drive. This requires the whole array to be 
regenerated, which is quite time consuming.

Is there a way to force the kernel to NOT assemble an array that's missing 
disks at boot time? The raid456 module is compiled into the kernel because 
this raid array is the root filesystem. I'm not using an initrd and want to 
avoid doing so because that's a nuisance.

Kernel version 2.6.27, if it matters.

TIA,
Aaron