Coppying lib (350GB) to an external drive failed

Since my iMac is becomming full, while my lib grows (350GB) i thought to move the lib to an extrenal drive. This failed twice on diferrent drives,1tb.
Story: My lib contains everything (+ masters). First I bought a WD MyBook essential (Mac journaled) and faced the problem that after fast copying of approx 1 GB the copying speed turned down tremendously (a few MBs /minute) and the remaining copying time went up to a 100 h!!. I stopped copying. The diagnose tool showed me no errors on the drive. In the shop I bought the drive they changed it to an Hitachi 1tb drive. But after installing the drive (also mac journaled) the same problem occured?
Whats wrong?
Is it not possible to copy such big files.
Do I have more chance with NTFS (how to re-format)
Is it in general a good idea to work with such a big lib on an external drive with usb 2.0.
In former times I worked with having just the masters on external drives, but after having too much broken links, I turned to put the complete lib on the iMac (24", 640GB).

Get FW800 drives, and let the copy operation run.  The reported copy time will drop.  It may still take a long time (but easily less than a day) to copy everything.  A 350 GB Library could have well over a million files in it.
Do not use any drive format other than Mac OS Extended (Journaled).
In short, there is nothing wrong.  You need a bigger pipe (FW) and more patience.
You will likely experience faster Aperture performance if you leave your Library on your system drive and move your images' Masters to your external drive (thus changing them from Managed to Referenced).  This is a bit of an administrative hurdle (things to learn, and you'll need a non-trivial back-up regime), but you reached the point at which it is time: your Library has outgrown your system disk's storage capability.
You might be able to run Aperture with acceptable performance with just your Masters on an external USB drive (I'd import new Masters as Managed, and move them to Referenced after 45 days or so, and leave all 5-star images' Masters as Managed), but I don't think you'll ever get acceptable performance with your entire Library on a USB drive.

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