I'm running El Capitan on a 2013 iMac. I need to copy a lot of data from several external USB 2.0 drives (Windows NTFS format) to several 3GB external USB 3.0 drives (Mac OS Extended Journal format). This data is "mission critical" and I need to be 100% sure that it copies correctly. Whats the best way to do this? Are there any Mac programs that copy and do checksums to verify the data integrity of the copy? Or is there anything build into OS X that can do this natively? For reference, on Windows I use a backup program called SyncBack to do this kind of thing. Thanks.