Hello [NAME] , Ok, so first, you may want to check this document: Dell EMC Tape Compatibility Matrix   In page 7, you can find the Dell EMC ML3/ML3E and all supported HBA's. And as the ML3 supports LTO8, LTO7 and LTO6 you can see it can be supported by the R640. So you just need to make sure when ordering the server to choose the correct hardware configuration.   I strongly recommend you to use our Partner Network. They will assist you configuring your hardware and offer you the better option to suit your needs. You can use this search engine.   Hope this helps. Please, don't hesitate to write us back if you have more questions. Regards.
I'm planning to order a server and a tape library from Dell. How ever, in R640 technical guide I found: "The R640 does not support internal tape drives, however, external tape backup devices are supported.Supported external tape drives:• External RD1000 USB• External LTO-5, LTO-6, LTO-7, and 6 Gb SAS tape drives• 114X rack mount chassis with LTO-5, LTO-6, and LTO-7 6 Gb SAS tape drives• TL1000 with LTO-5, LTO-6, and LTO-7 6 Gb SAS tape drives• TL2000 with LTO-5, LTO-6, and LTO-7 6 Gb SAS tape drives• TL4000 with LTO-5, LTO-6, and LTO-7 6 Gb SAS tape drives• TL4000 with LTO-5, LTO-6, and LTO-7 8 Gb FC tape drives• ML6000 with LTO-5, LTO-6, 6 Gb SAS tape drives• ML6000 with LTO-5, LTO-6, LTO-7 8 Gb FC tape drives" So I wonder if is PowerVault ML3/ML3E Tape supported by R640 ?  Because Tape Library required "1 x LTO8 SAS drive, 40 Slot, SAS Cable 6Gbps, 31 x LTO8 Tape media with bar code label attached, 1 x LTO Cleaning Media" , there is no other better option.  
Is PowerVault ML3/ML3E Tape supported by R640