External Drive

[#1]

You might a couple of these to be useful

http://www.ebuyer.com/754119-integral-128gb-3-0-usb-stick-infd128gbblk3-0

The write speed will be slow, though

[#2]

One issue to be aware of with external drives, is that whilst they usually have a standard SATA disk inside, if the enclosure dies, you may well lose all of your data. You can't simply extract the disk and connect it internally to the PC.

For Seagate, I believe the issue is just to do with how they handle backwards compatibility of large drives (so this may be recoverable by just putting in a replacement enclosure of the same type), but for the Western Digital MyBook, the data is encrypted, and the encryption key is tied to the enclosure. So basically, if a WD enclosure dies, all of your data is gone, with no chance of recovery, even if the disk itself is fine. The WD MyBook Duo is a really stupid product in that respect, because the redundancy of offering two disks is completely nullified by having a single point of failure in the enclosure.

If the photos are really important, then I would either buy two disks, so you have a backup, or make use of something like Amazon Cloud Drive. I wouldn't trust any cloud services to hold my only copy, due to their tendency to change their mind about how much they want you to store, but it's great for an off-site backup.

[#3]

You don't have to use the supplied backup software on external disks; just wipe the external disk and format it as a standard file system.

[#4]

With the WD MyBook range it doesn't matter what software you use - all data is encrypted on its way to the disk by hardware in the enclosure, and since it's AES 256, your chances of recovery are practically zero, unless you have friends at GCHQ.

For that reason, I only use them for storing parity data - if they do die, there is nothing of value that I would either need to recover, or would want to wipe before sending in for RMA in the event of failure.

The situation with Seagate isn't quite as bad - the data is mangled a bit by a translation layer (for Advanced Format/4K/2TB support), but you supposedly can at least recover it with some software, such as Seagate's own.

I've tried a few external drives - my favourite so far is the Seagate Expansion Portable. It's powered by USB 3.0 (no mains adapter), small, quiet and cool-running. I have the 4TB model, but I believe it also comes in smaller capacities. It's designed to lay down, so no chance of knocking it over.

Avoid the 8TB LaCie and Seagate disks - they run far too hot (the 4TB 5940RPM model is acceptable). I ended up extracting the disks from these to use internally - they require proper airflow and the cases they come in are not fit for purpose.

Likewise avoid anything with a 7200RPM disk in it - again too much heat for the small passively-cooled cases they come in. The Hitachi Touro Desk is fine (5400RPM disk) but the Touro Desk Pro runs a bit hot. Most Seagate are 5940RPM now, but they do have a few 7200RPM models.

I agree that a USB SSD is false economy. They're more likely to survive a drop or being knocked over, but you're very unlikely to benefit from the access time improvements, and sequential read/write of modern spinning disks are more than good enough.