Prices are coming down on storage arrays for home and small business and new units are packing in the features.
Do you have a home network with more than one computer, or do you find you are constantly running low on harddrive space? Have you ever lost your critical data due to a virus, software failure, or hardware failure?
The answer is to get a network storage array. The problem with single portable USB drives is there is no backup - so if they take a bump or fail, the data is gone.
Network Attached Storage (NAS) is a box that is dedicated to storage. Its usually a computer running some form of Linux that is setup to manage networking and storage. They come in a variety of sizes, from 1 harddrive upward.
Some of the newer arrays come with software allowing connections via iSCSI (a very fast network protocol shared with one computer and mapped as it the space was a local drive). Other features they often have are ftp servers, web setup interfaces, torrent downloads, media server (for those new DLNA devices which allow direct streaming of video and music), iTunes server, Photo Serving, and wireless access. They of course can also act as storage for backups (some even have auto synchronizing backup software) and general file storage.
Using more than 1 drive in these units allows you to use various RAID levels. Raid 1 uses two drives and mirrors the drive (so if you have two 500 Gig harddrives, you have 500 Gigs of storage in a Raid 1 configuration but if one drive fails, the data is still available from the second drive). Raid 5 uses three or more drives. It uses a striping/checksum method that is tolerant to one drive in the array to fail. It will rebuild on the data on the failed drive when replaced.
There are other Raid configurations available, but the ones listed above are the most commonly used.
Some of the arrays I have used are from Thecus. They are one of the better arrays for speed, have really good web interfaces, and are expandable. They are not the cheapest brand to get, but are a very strong value.