External hard drives are external peripherals that comprise a standard desktop or notebook hard drive contained within a portable enclosure that provides one or more types of interface connector to link the external hard drive to a desktop or notebook computer. Many external hard drives include backup software that features a "one-button" means of backing up data from your internal hard drive. External hard drives may use any of three interfaces: USB 2.0, FireWire, and External SATA.
USB 2.0
USB 2.0 is by far the most common interface supported by external hard drives. USB 2.0 nominally provides 60 MB/s bandwidth, but overhead typically reduces this to an effective 25 MB/s to 30 MB/s. Because standard hard drives can use 50 MB/s or more bandwidth, the USB 2.0 interface throttles throughput noticeably for the fastest external hard drives, making them "feel" somewhat slower than an internal drive. The advantage of USB 2.0 is that it is ubiquitous, so a USB 2.0 external hard drive can be connected to nearly any notebook or desktop system. Although data corruption is possible with any external hard drive, it is particularly likely to occur with USB 2.0 external hard drives. Data corruption occurs if the drive is turned off or disconnected before buffered data is written to it. To avoid data corruption, always flush the buffer before you turn off or disconnect the drive. To do so, use the Windows Safely Remove Hardware Wizard, which notifies you when it is safe to remove the drive.
FireWire
FireWire (IEEE-1394a or IEEE-1394b) is similar functionally to USB 2.0, but faster in real terms. Most FireWire external hard drives use IEEE-1394a S400, which provides nominal bandwidth of about 400 Mb/s, or 50 MB/s. True throughput is somewhat smaller, but sufficient to make throttling relatively minor. Most IEEE-1394b external hard drives support the S800 data rate, which eliminates throttling completely. The disadvantage of FireWire is that relatively few systems, notebook or desktop, provide an S400 FireWire interface port, and almost none provide an S800 port. Few FireWire-only external hard drives are available. Most drives that support FireWire also include a USB 2.0 interface. If you plan to use a small FireWire drive with your notebook computer, you'll probably want bus power. Not all FireWire ports deliver bus power.
External SATA
External SATA (eSATA) is the least common interface supported by external hard drives, but is fast gaining popularity. eSATA provides 150 MB/s or 300 MB/s bandwidth, and the high efficiency of the eSATA protocol means that nearly all of that bandwidth is actually available to the drive. An eSATA external hard drive has the same performance as the same drive used internally. The disadvantage of eSATA is that only a tiny percentage of systems have eSATA ports. You can add eSATA support to an existing system by installing an eSATA host bus adapter in a desktop system or by using a Cardbus or ExpressCard eSATA card in a notebook. For desktop systems, you can instead use an inexpensive adapter that connects to an internal standard SATA port and provides an eSATA port on an expansion card bracket.
Broadly speaking, there are three categories of external hard drive: full-size external hard drives, portable external hard drives, and Pocket external hard drives.
Full-size external hard drives
Full-size external hard drives are about the size of a thick hardback book (or a Mac Mini). Because they use standard 7200 RPM 3.5" desktop ATA or SATA drives, these drives have high capacitiesfrom 120 GB to 500 GB or moreand very high disk performance. They are readily available in USB and/or USB/ FireWire interfaces, and by mid-2006 will be available in eSATA models. Because full-size external hard drives use standard 3.5" desktop hard drives, they require more power than can be provided by the interface cable. Accordingly, full-size external drives always use a power brick.
Portable external hard drives
Portable external hard drives are smaller than a paperback book, and about an inch thick. Because they use 4200 RPM 2.5" notebook hard drives, these drives have smaller capacitiestypically 40 GB to 120 GBand lower disk performance than full-size models. Their low power consumption means they can be powered directly by the interface and so require no power brick. Most portable models are USB-only.
Pocket external hard drives
Pocket external hard drives are a solution in search of a problem. Because they use 3600 RPM 1" hard drives, these models have tiny capacitiestypically 5 GB or lessand much lower disk performance than even portable models. We see no point to buying one of these drives. USB flash drives, described later in this chapter, are smaller, faster, cheaper, and hold more data.
External hard drives of various types are made by Iomega, Maxtor, Seagate, Western Digital, and other companies. We prefer the Seagate models.
External Drive Enclosures
You don't have to buy an external hard drive; you can roll your own. External drive enclosures are an economical alternative to commercial external hard drives, which sometimes sell at a high premium over the cost of a bare hard drive. These enclosures, most of which cost $20 to $40, accept standard ATA or SATA drives and provide internal power and data connectors for the drive. They also include ATA-to-USB and/or ATA-to-FireWire interface circuitry and an external jack or cable by which the enclosure can be connected to a PC. Models that accept 2.5" notebook hard drives are powered by the USB cable (usually a USB Y-cable, which draws power from two USB ports) or a 6-wire FireWire cable. Models that accept 3.5" hard drives use a separate power brick to supply the higher current needed by standard ATA/SATA hard drives.
Installing a hard drive in one of these enclosures is easy: you simply open the enclosure, secure the hard drive with the supplied mounting screws, connect the internal power and data cables to the drive, and put the cover back on the enclosure. Most enclosures use rubber shock mounting and other means to protect the drive if the enclosure is dropped.
One advantage to rolling your own is that commercial external drives usually have only a one-year warranty. If you build your own external drive with an enclosure and a standard hard drive, the drive has its standard warranty, which may be as long as five years.
External drive enclosures are made by Belkin, IOGEAR, Kingwin, ThermalTake, Vantec, and others, and are widely available online and at big-box retailers. Price is a good indicator of quality. The $20 units we've seen appear fragile and shoddily made. The $30 and $40 products use more metal and less plastic, and appear to be considerably more reliable. The better units sometimes include a cooling fan, which may improve the reliability and service life of the drive.
Some external enclosures can also accept a DVD writer or other drive that uses removable media. If you mount a DVD writer in such an enclosure, make sure the power brick is rated to supply the peak amperage required by the drive, which may be considerably higher than the draw of a hard drive.
External Drive Repair
Whenever a external hard drive has a problem, first of all, what you have to do is the hard disk diagnostic. Hard disk has bad track In addition to the quality of the hard disk itself, as well as the aging, usually not be able to treat the hard disk, such as too little memory caused application software frequently visit hard drive, too frequently defragmented, frequent partitions, formatting, improper over clocking, Power quality is not good, the temperature is too high, undesirable dust and vibration. Bad Track is divided into two kinds of logical bad sectors and physical bad sectors, the former for soft bad sectors, usually caused by improper operation or use of the software,
Software repair; the latter is a real physical bad sectors, it shows that the hard disk track generate a physical injury, only by changing the hard disk partition, the use of sector or to hide to resolve. The following are steps to troubleshoot the external hard drive:
1. Check whether the department have power supply.
2. Connection (Cable) is connected correctly or not.
3. Check the settings. Disk Select Jumper(Master/Slave).
4. Check the installation (set up) is correct or not.
5. Check whether you need a hardware or software fix. Look for grinding sounds from your drive or humming that starts or stops. These are signs that the actuator arm and discs are no longer in alignment and your drive is timing out. If it seems as though nothing is wrong with your hard drive, it's probably time for a software fix.
6. Run one of the many software fixes, if you think the problem is related to software. These programs feature on-screen directions, making it easy for you to progress through them. If this works, you don't need to fix a physical problem.
7. Remove the many tiny screws that holds the drive together. Eventually, you'll get to the innards of your drive. Be very careful not to bend or force a piece to go where it doesn't want to.
8. Determine if you've set things straight. Look to see whether anything was loose inside your external hard drive. If you have recently dropped it or traveled with it, it is possible that something came loose. Also check that all the arms and platters are straight and do not appear bent in any way. If they are bent, straighten them with your hands or pliers.
9. Put everything back together and check that everything in your external hard drive is working properly.
10. Try using the external hard drive on another computer. Maybe your computer or USB port is the problem and needs replaced.
11. You should know that drive failures are caused by the following factors:
1. PCB Fault.
2. Motor / Bearing Fault.
3. Kai / stop system failures.
4. Read / write head failure.
5. Failure and surface scratches head.
6. Bad Sector.
7. Part or all of the firmware data loss.
To protect your external hard drive from damage and the safety of your data, you should keep the following in your mind:
1. Make an emergency boot disk. Safe this disk in a safe place just in case - you¡¯ll be glad you took the five minutes to prepare this disk. Also, save a copy of your config.sys file. You can create this emergency boot disk with your copy of your Windows operation system.
2. Use the utilities that come with your system. It's important to run your Disk Defragmenter on occasion. You can even schedule Windows to perform this task on a regular basis. This will consolidate data and reorganize your drive. It will free up space, improve performance and prevent errors.
3. When you are ready to delete a program, do not go into the folder and start deleting it that way. You¡¯ll never get rid of all the components and this can cause a real disaster for you. Use the Add/Remove function in the Windows Control Panel.
4. Back up on a regular basis. No, you do not need to back up your whole hard drive, just important data and files that you change on a regular basis. This can be done through using an internal or external drive, USB drive, removable media, or even using an Internet-based backup service where you run a program and it uploads your backups to another server located on the Internet for storage.
5. Try not shut off your computer with the power switch or power cord. Take it down through a system shutdown from your Start button. This ensures that everything closes properly and readies your system for reboot.
6. Use the Windows Safely Remove Hardware Wizard to turn off your external hard drive.
When the above steps are followed, you are likely to avoid the most serious problems. However, when you simply cannot get back those lost files, you can use data recovery software to get back your lost files and data and restore your computer.
