We installed flashcache on Debian jessie onto a softraid.
When booting the machine it hangs up in initramfs and we had to manually load the flashcache. Then the boot continued successfully.

It seemed the problem was that the flashcache_scan initramfs script was executed before the mdadm script so the raid was not yet assembled.
I could resolve the problem by moving the flashcache_scan script from init-premount to local-premount.