Compatible With: M521dn [HPL5521], M521dw [HPL5522]. NBD = Next Business Day, DMR = Defective Media Retention. When hardware issues come up, the sooner you can get running again, the better. Have expertise at the ready with HP Next Business Day Onsite Service with Defective Media Retention, and vastly improve your product uptime. With high-quality remote assistance and convenient onsite support available the next business day, help is there when you need it – so you can get back to work. When dealing with failed storage media, you maintain control of your sensitive data.