Hot answers tagged external-disk
Short Story: Use DiskWarrior My computer crashed and damaged directory files on my external hard drive. So it wouldn't mount but I could see it in Disk Utility (altho it wouldn't repair). Paid the $120 for the diskwarrior, went thru everything and it was fine. Gives you a preview to grab files too before they go in and fix the bug. Worth the money.
You could use rsync like this: rsync -av --delete /Volumes/DiskA/ /Volumes/DiskB --delete option is for delete files in DiskB that was previously deleted on DiskA. If you want to schedule it to execute periodically, I suggest you to read How can I run/stop/relaunch an application automatically, at boot/login/some other time?.
rsync is certainly one way to go. The other is to use something like SuperDuper or CarbonCopyCloner which can do drive cloning/mirroring. Also, ChronoSync might be an option as well, if you need to keep track of deleted contents for any reason.
I use DropSync and have done for ages - does what you need and more and costs $8 http://www.macupdate.com/app/mac/33071/dropsync
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