Weighing the options: Pros and cons
Capacities Price Range/Per GB Pros Cons Best uses
Two internal drives in a RAID 1 array 500GB to 3TB $60 - $400 for second drive, depending on capacity/$0.13 -$0.17 per  GB Fastest; can buy a PC preconfigured this way; no software is required; backups are immediate and automatic; large capacity; prevents data loss from a single drive failure. Susceptible to malware, home theft, or disaster; one entire drive is dedicated solely to backup; can't recover accidentally deleted or overwritten files. Immediate, automatic, hassle-free backups.
External Hard Drives 500GB - 3TB (single drive) $85 - $400/$0.13 - $0.17 Fastest for large capacities; inexpensive; connects via USB, firewire or eSATA; smaller models may require no external power. Susceptible to malware, home theft, or disaster; must configure and run backup software. Primary storage of large amounts of data.
Network Attached Storage 1TB to 80TB+ $100 - $2000+ Fast for large capacities;  no software is required; backups are immediate and automatic; extremely large capacity; prevents data loss from a single drive failure. inexpensive; connects via Ethernet to be accessed shared by more then one computer. can be accessed from remote locations for field workers. Data backed up across multiple drives for backup. Susceptible to malware, theft, or disaster; At least one entire drive is dedicated solely to backup; Maybe able to recover accidentally deleted or overwritten files. Can be accessed/hacked from remote locations across the internet if not properly secured. Primary storage of large amounts of data. Immediate, automatic, hassle-free backups.
Flash Drives 8GB -128GB $15 - $220 Small; portable; connects via USB; requires no external power. Easy to lose; size makes labeling difficult; must configure and run backup software for easy successive, incremental backups. Limited storage; secondary backup.
Optical Media 700MB (CD) - 50GB $0.22 (CD-R) - $50 (Blu-Ray double-sided DVD) With the exception of Blu-Ray, discs are very inexpensive; most computers have players/burners; easy to use. Slow; limited capacity; susceptible to scratches and physical damage; discs can't be read by all drive types; incremental backups require special software. Archiving songs, video, and photos for use on consumer electronics devices.
Online Backup Services 250MB - unlimited Free - $64.95 per month Unlimited storage potential; most secure; nothing to break; safer from theft than local backup; remote file sharing is possible. Slowest; monthly fees can be high; requires fast, reliable Internet connection; must trust site's security, longevity.

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