Sharing storage between several computers can be done with a networked attached storage (NAS) system. Commercial offerings are usually expensive, even for the low end, but is it easy to make one with an old or new computer.
Hardware
Building an NAS does not require a lot of processing power, and even a old computer will be sufficient. However, because an NAS will be on often, you may want to go for a low-power system to avoid an increase in your electric bill. Intel and it's ATOM line of CPUs have a very efficient and cheap platform to start with, but the system cannot accept more than two hard drives. AMD, like Intel, has a low-power mainstream processor. At 35W, they consume half to one-third of the power compared to other processors on the market. Take a motherboard with at least four or six hard-drive ports, an integrated video card and 2 GB of memory.
Storage
You will have several options for storage on the NAS. Because you are using the network to access the data, you do not need to buy high-end fast hard drives. The network will be the bottleneck. Instead, you may want to buy a "green" hard drive that uses less power than regular ones. Redundant Array of Inexpensive Disks (RAID) is a way to group hard drives in order to have more speed, fault tolerance or both. If you are storing important data on your NAS, you may want to use RAID. For data safety, you will want to use RAID 1 or RAID 5/6. RAID 1 works with two hard drives, mirroring one to the other, therefore loosing the equivalent of one drive worth of space. RAID 5/6 are for when you use more than three (RAID 5) or four (RAID 6) drives and works by creating one (RAID 5) or two (RAID 6) parity drives. If one of the drives is faulty, the system uses the parity information to rebuild all the data. Most RAIDs will require you to use identical hard drives.
RAID
In order to manage a RAID, you will have to choose between software RAID and hardware RAID. Both software and hardware RAID will provide the same function, but will do it differently. Software RAID will use the processor to make all the calculations that will impact the performances of the system. Hardware RAID will use the dedicated processor and memory on the card to do the calculations. Some RAID cards will also feature a small battery to allow for the card to finish writing data if a power outage occurs and therefore avoid RAID corruption and the loss of data. The cost of a RAID card is not negligible at $300 to several thousand dollars as of 2009.
Network
A regular 100 MB network will transfer a DVD of 4 GB in a little over six minutes. A 1,000 MB network will take 40 seconds. A Wireless N network will transfer the same DVD in six minutes and wireless G will do the same in 30 minutes. Depending on the use of your NAS, you can choose what type of network will be best for you.
System
You will need to install an operating system on your NAS. You can use Windows or Linux if you like or use NAS-specific free operating system like FreeNAS or Openfiler. Both are free, and easy to install and manage. The main difference between the two operating systems is the support of iTunes and torrent downloads on FreeNAS and the option to buy support for Openfiler.
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