Regarding the perceived fragile nature of internal drives in external caddies...

3.5" drives were never intended to be carried around, the 2.5" drives fitted in laptops and portable external units are far more resilient.

I would suggest that a drive taken out of a PC and installed in a caddy is no more likely to fail than a similar hard drive OF THE SAME AGE that has been in a caddy since new.

A drive in a caddy may fail prematurely if:

1. The drive is moved whilst switched on, particularly if it is in a read/write state.

2. Switched on and off frequently - they are more stable if kept at a constant temperature, as are many electrical items. Startup current is usually the killer!

3. Treated roughly even when switched off.

4. Inadequately cooled - some drives run hotter than others, and a caddy may not dissipate suffient heat whereas the same drive in a PC case would have the advantage of fan cooling.

5. Subjected to extended data transfer... often, when a drive has been fitted in a caddy, the next step is to copy all the data from (or to) it, which may take a few hours. A drive is normally expected to cope with intermittent data transfer, allowing it to cool properly.

Well, that's my take on it, anyway!