The button below 'RECALL' is for recording. There is a user manual on the website x2sat.com that has instruction, they are better than none... I don't have a USB hard drive, but I did put a 16GB flash drive in it and recorded an hour of ABC last week, and it played back just fine. If there is a max size, it is bigger than 16GB. An hour of ABC at 720P uses 6-9GB. I used the timer to get the recording, but I guess pushing the button would do as well.
Migold -
10' Mesh BUD Dual C-LBNF (61W-139W) with (1) Dual LNBF for 97°W & (2) Dual LNBF for 101°W; 90 cm GeoSatPro w/ DG380 (61W-125W) & 2.4 meter stationary (aimed to) with (1) Dual C-LBNF for 99°W & (2) Dual LNBF for 105°W. 4X4 switches w/ DiSEqC switches to AZBOX Premium Plus HD; AZBOX miniMe; X2 mini Premium HD, & X2 DVB-S2 M1 HD. OTA-VHF Hi-Band Yagi+Amp; HDTV Antenna w/Internal Booster from 'antennashopusa' on ebay.