Guide to Buying External Storage

If you edit movies, take lots of digital photos, play games or listen to music files on your PC, a big, fast internal drive might not suffice. For more storage or a means to back up your PC's internal drives, you can add an external hard drive. And if you want centralized storage, consider buying a network-attached storage (NAS) device.

The Big picture

An external, direct-attached drive uses the same basic mechanism, but it's housed in an enclosure that connects to your PC via the USB 2.0, FireWire or eSATA bus. Another option is an external NAS device that connects to your router via Ethernet. NAS devices are continually improving and can be a convenient way to add storage that all of the PCs on your small or home network can share.

Detachable external drives are more versatile than internal drives: They let you add storage capacity to a PC whose internal drive bays or connections are maxed out. And you can share an external drive among multiple PCs and store it in a safe place when using it as backup media.

2.5-in. or 3.5-in. drive: The newest range of plug-and-play portable drives is predominantly based on 2.5-in. drives and provides enough capacity to hold a decent sized digital library. However, if you want a huge-capacity drive, look for a 3.5-in. model. For most people, the smaller size of a 2.5-in. drive is worth the loss of capacity; an external 2.5-in. drive is small enough to fit into a pocket, whereas an external 3.5-in. drive can only be considered portable if it comes with its own carrying case.

NAS: This allows easy access from any PC attached to your network and can be placed in a relatively safe location. Some multiple-drive, high-capacity NAS devices offer perks such as printer and Internet file access so you can share printers across the network or access files from anywhere on the Web. NAS's biggest drawback is that you need to transfer data via Ethernet, which generally makes it the slowest option.

Flash-based drives: Flash-based solid-state drives (SSD) are best in terms of portability. They connect to your computer via USB2.0, and most don't even require an additional power adapter. They don't heat up as much as their spinning drive counterparts, and they are much more stable. On the flip side, transfer speeds are slow compared with 2.5- or 3.5-in. In the end, hard drives are either all about capacity or all about speed -- depending on your needs. Our tests show that all of today's hard drives perform adequately when running regular home and business applications. Nevertheless, capacious, speedy drives particularly benefit people who process large files, images and digital video.

Specs Explained

Given below is the lowdown on the specs that matter, and the ones that don't.

Important: capacity. External direct-attached drives come in capacities of up to 1TB for single-drive models; some manufacturers achieve the same total capacity with two 500GB drives or four 250GB drives striped together in a RAID 0 or disk-panning configuration. Portable external drives, which use a notebook-size 2.5-in. hard disk, currently max out at 500GB. It's wise to go for as much capacity as you can afford -- especially for a NAS device, since multiple users are likely to fill it relatively quickly.

Important: rotational speed. Portable external drives have the biggest range in rotational speeds, and the faster the rotational speed, the faster the drive. Models are currently available in 4,200-, 5,400- and 7,200-rpm flavors. The most common of these is 5,400 rpm. You'll see a difference in transfer speeds if you copy a lot of data -- say, photos from a full 2GB memory card -- to your hard drive, so keep a close eye on these specs, and beware of vendors that don't identify the drive's rotational speed

Important: interface. Be very careful about the drive's interface, because it's a factor that predominantly decides what data transfer speeds you will end up with. Most external drives have a USB 2.0 interface or a dual USB/FireWire interface. Other interface configurations are dual USB2.0/FireWire 400, FireWire 800 and eSATA. For high-performance external storage, go with an eSATA direct-attached drive. These drives are becoming increasingly popular. Although they don't offer the universal connectivity of a USB 2.0-enabled drive, they're as fast as an internal drive.

To install an eSATA drive, you'll need an open external port. Though eSATA drives come with a pass-through connector that provides an external port, you'll need an open internal SATA port to attach the connector to. If not, an inexpensive PCI add-in card can provide external SATA, USB 2.0 or FireWire ports for systems that lack them. Consumer-level NAS devices generally employ the TCP/IP protocol and a 10/100 Base-T or Gigabit Ethernet connection to hook up to your network. Look for NAS devices that provide USB 2.0 ports for accommodating additional hard drives so you can expand capacity or share attached printers across the network.

Somewhat important: seek speed. Average seek speed, measured in milliseconds, refers to how fast drives can find a particular piece of data. This is a minor consideration: For most people, the effect of differences on this measure in everyday use is negligible. The exception is when a drive is called upon to assemble many small pieces of data scattered in different areas of the hard drive, such as when copying large folders full of many small files. Jumbo drives tend to have somewhat longer seek times.

Somewhat important: buffer. When a system requests data, a hard drive will fetch what is requested and load its buffer memory with extra information that the processor is likely to ask for next. Theoretically at least, a larger buffer size should help keep the data flowing better, especially in disk-intensive tasks such as file searching. Buffer sizes range from 8MB to 32MB.

Somewhat important: RAID setup. RAID 0, the most common setup, delivers faster performance by splitting data across multiple drives. Its drawback is that if one drive fails, the data on all drives is lost, so you'll need to keep your backups current. For systems that need to minimize down time, RAID 1 -- in which data is written redundantly or mirrored across multiple drives -- is a popular alternative. If a drive goes bad, the system can continue to run on a good one until you have the opportunity to install a new drive.

Buying Tips

Are you ready to take the plunge and buy a big new hard drive for your PC? Here are our recommendations for what you should consider.

Flash for portability: Flash-based drives, as explained earlier, are slower than spinning disk-based 2.5-in. or 3.5-in. drives, but they are extremely portable; most fit easily within a trouser pocket. They connect via USB 2.0.

Notebook drive: External models that use hard drives intended for laptops tend to be optimized for mobile use. One relevant feature is a durable enclosure with a high shock rating, meaning that it can absorb a typical impact from a desk to the floor, for example.

RAID 0 or 1: RAID 0 is the way to go for performance hounds, but RAID 1 can take care of your data security concerns. Ideally, try to get a RAID-configurable drive, but they cost more.

Make sure the external case you buy supports USB 2.0 or eSATA ports. If they throw in a FireWire port, great!

Consider a NAS device.

They're a great choice for backup as well as for making photos, videos, music and other files available to everyone on your network. NAS devices connect to your network via Ethernet, which means middling performance, but in most cases, they also include USB 2.0 ports to share a printer or to expand storage capacity.

Copyright © 2008 IDG Communications, Inc.

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