i tried with nas but i could never make it work and when i asked my supplier tech , he said its not reliable ,hard to work ,and forget it, but i had a situation to install one camera only , i had no intention to buy nvr for one camera , so
i bought a camera(hikvision) that support sd card and loaded 64 gigabyte , it records for couple days , but i wanted to keep the record for more , so i started to look for a back up software after search i found that software Hikvision iVMS-4200 PCNVR
http://www.hikvision.com/en/download_more.asp?id=1190
what it does it downloads the record from the sd card to a computer , u set it up , and the good thing , computer doesn't have to be up all time , and also it playback , and live view i use web interface , it works good everyday they turn on their office computer , the programe starts to download all the record , i couldn't get to use all the feature on it cos it's not friendly interface i wish if some one explain more about it
hope that could be useful for u