[Hampshire] NAS devices and MTU

Hi all

Season's greetings.

Can anyone help fill (one of many) gaps in my networking knowhow?

I got a Netgear ReadyNAS Duo for Christmas and performance has been really slow. It seems the MTU is the culprit. Two problems:
1) Should the MTU on the NAS (I've only ever seen MTU on routers before) be set to the same as the MTU on the router?
2) It seems the ReadyNAS insists on setting its own MTU as I've told it to "Auto-negotiate" the Speed / Duplex mode. The other two options for this setting are full or half duplex at 100MBps. I tried both of these yesterday which resulted in the ReadyNAS basically dying and only a factory reset brought it back so I'm loathe to do it again.

And this brings me to a 3rd question come to think of it....

3) Is it the MTU that will be affecting performance or is this a red herring?

Cheers
Rob