Advice is like opionions, everyone has them. I use ESata and USB, without a problem.
I use an AZiO ADP-SU33, USB2.0 & eSATA HDD Docking Station, and an external USB2.0 & eSATA HDD enclosure. The only drawback issue has been the ESata is not "hot-swap".

Other's on this forum would advise you not to use external drives, and I would agree with that in regard to 24/7 usage. I now 2 Seagate 1T (ST31xxx340AS) that are 2 yr old bricks. Both were on 24/7. Could have been it was the problem with the 7200.11 CC34 revision's.

I also have 4 Seagate 1T (ST31xxx528AS). One is in my computer, and 3 are on standby, clones of my system. The clones are shelved.

My suggestion: Check with Dell (they have been exceptionally helpful recently) concerning any BIOS or MOBO issues with a 2T. Then replace your internal drive by cloning. Try to eliminate some of those external drives by combining into either 1T or 2T. Then back up those partitions (data) to the older drives your going to shelve off-line.