According to the Wikipedia page external SAS cables are specified for up to 10m length.

However, I found it pretty hard to actually find places that sell cables of that length. This made me wonder:

Are there any known problems with using cables that are as long as this? Will it be more fragile? Slower?

And if 10m is not suggested, would 6m be any more stable?

A little background: for several reasons we'd like to put a tape library physically separate from our main server and 10m would be enough to put it on a separate floor.