For Brother Printers, The drum unit transfers toner powder from the toner cartridge to the page. This usually happens after the drum unit has been used for a couple of toner cartridges. DR-630 drum unit capacity of 12,000 pages and needs to be replaced after the use of 3 or 4 replacement toner cartridges. Buy replacement toner cartridges online from Linkyo to ensure a 100% Satisfaction Guarantee.