HARD DRIVE TECHNOLOGIES AND INTERFACE STANDARDS

hard disk drive (HDD)

A hard disk drive (HDD), most often called a hard drive, comes in two sizes for personal computers: the 2.5" size is used for laptop computers and the 3.5" size is used for desktops. See Figure 6-1. In addition, a smaller 1.8" size hard drive (about the size of a credit card) is used in some low-end laptops and other equipment such as MP3 players.

RAID

A technology that configures two or more hard drives to work together as an array of drives is called RAID (redundant array of inexpensive disks or redundant array of independent disks). Two reasons you might consider using RAID are: To improve fault tolerance, which is a computer's ability to respond to a fault or catastrophe, such as a hardware failure or power outage, so that data is not lost. If data is important enough to justify the cost, you can protect the data by continuously writing two copies of it, each to a different hard drive. This method is most often used on high-end, expensive file servers, but it is occasionally appropriate for a single-user workstation. To improve performance by writing data to two or more hard drives so that a single drive is not excessively used.

Sata

All hard drives in today's personal computers use the SATA interface standards to connect to the motherboard. The serial ATA or SATA (pronounced "say-ta") standard uses a serial data path, and a SATA data cable can accommodate a single SATA drive

low-level formatting.

Before a magnetic drive leaves the factory, sector markings are written to it in a process called low-level formatting. (This formatting is different from the high-level formatting that Windows does after a drive is installed in a computer.) The hard drive firmware, UEFI/BIOS on the motherboard, and the OS use a simple sequential numbering system called logical block addressing (LBA) to address all the sectors on the drive. SSD drives are marked into blocks, which are communicated to the motherboard and OS, which read/write to the drive in blocks just as with magnetic drives.

E-SATA

External SATA drives use a special external shielded SATA cable up to 2 meters long. Seven-pin eSATA ports run at the same speed as the internal ports using SATA I, II, or III standards. The eSATA port is shaped differently from an internal SATA connector so as to prevent people from using the unshielded internal SATA data cables with the eSATA port.

external enclosures

Hard drives are sometimes stored in external enclosures such as the one shown in Figure 6-33. These enclosures make it easy to expand the storage capacity of a single computer or to make available hard drive storage to an entire network. For network attached storage (NAS), the enclosure connects to the network using an Ethernet port.

Hybrid Hard Drive

Hybrid hard drives. A hybrid hard drive (H-HDD), sometimes called a solid-state hybrid drive (SSHD), uses both technologies. The flash component serves as a buffer to improve drive performance. Some hybrid drives perform just as well as an SSD drive. For a hybrid drive to function, the operating system must support it.

Magnetic hard drive

Magnetic hard drive. A magnetic hard drive has one, two, or more platters, or disks, that stack together and spin in unison inside a sealed metal housing that contains firmware to control reading and writing data to the drive and to communicate with the motherboard. The top and bottom of each disk have a read/write head that moves across the disk surface as all the disks rotate on a spindle (see Figure 6-3). All the read/write heads are controlled by an actuator, which moves the read/write heads across the disk surfaces in unison. The disk surfaces are covered with a magnetic medium that can hold data as magnetized spots. The spindle rotates at 5400, 7200, or 10,000 RPM (revolutions per minute). The faster the spindle, the better performing the drive. Data is organized on a magnetic hard drive in concentric circles called tracks (see Figure 6-4). Each track is divided into segments called sectors (also called records). Older hard drives used sectors that contained 512 bytes. Most current hard drives use 4096-byte sectors.

Solid-state drive

Solid-state drive. A solid-state drive (SSD), also called a solid-state device (SSD), is called solid-state because it has no moving parts. The drives are built using nonvolatile memory, which is similar to that used for USB flash drives. Recall that this type of memory does not lose its data even after the power is turned off. In an SSD drive, flash memory is stored on EEPROM (Electronically Erasable Programmable Read-Only Memory) chips inside the drive housing. The chips contain grids of rows and columns with two transistors at each intersection that hold a 0 or 1 bit. One of these transistors is called a floating gate and accepts the 0 or 1 state according to a logic test called NAND (stands for "Not AND"). Therefore, the memory in an SSD is called NAND flash memory. EEPROM chips are limited as to the number of times transistors can be reprogrammed. Therefore, the life span of an SSD drive is based on the number of write operations to the drive. (The number of read operations does not affect the life span.) For example, one SSD manufacturer guarantees its SSD drives for 20 GB of write operations per day for three years. For normal use, a drive would not be used that much and would last much longer. Many solid-state drive manufacturers reserve blocks on the drive that are used when blocks begin to prove they are no longer reliable. Also, a technique called wear leveling assures that the logical block addressing does not always address the same physical blocks in order to distribute write operations more evenly across the device. Because flash memory is expensive, solid-state drives are much more expensive than magnetic hard drives, but they are faster, more reliable, last longer, and use less power than magnetic drives. Figure 6-2 shows two sizes of solid-state drives (2.5" and 1.8") and what the inside of an SSD hard drive looks like. The 1.8" drives are used in some laptops and other small mobile devices.

Different types of RAID

Spanning, sometimes called JBOD (just a bunch of disks), uses two hard drives to hold a single Windows volume, such as drive E:. Data is written to the first drive, and, when it is full, the data continues to be written to the second. RAID 0 also uses two or more physical disks to increase the disk space available for a single volume. RAID 0 writes to the physical disks evenly across all disks so that no one disk receives all the activity and therefore improves performance. Windows calls RAID 0 a striped volumed. To understand that term, think of data striped—or written across—several hard drives. RAID 0 is preferred to spanning. RAID 1 is a type of mirroring that duplicates data on one drive to another drive and is used for fault tolerance. Each drive has its own volume, and the two volumes are called mirrors. If one drive fails, the other continues to operate and data is not lost. Windows calls RAID 1 a mirrored volume. RAID 5 stripes data across three or more drives and uses parity checking, so that if one drive fails, the other drives can re-create the data stored on the failed drive by using the parity information. Data is not duplicated, and, therefore, RAID 5 makes better use of volume capacity. RAID-5 drives increase performance and provide fault tolerance. Windows calls these drives RAID-5 volumes. RAID 10, also called RAID 1+0 and pronounced "RAID one zero" (not "RAID ten"), is a combination of RAID 1 and RAID 0. It takes at least four disks for RAID 10. Data is mirrored across pairs of disks, as shown at the top of Figure 6-27. In addition, the two pairs of disks are striped, as shown at the bottom of Figure 6-27. To help you better understand RAID 10, in the figure notice the data labeled as A, A, B, B across the first stripe. RAID 10 is the most expensive solution that provides the best redundancy and performance.

Hot-Swapping

With hot-swapping, you can connect and disconnect a drive while the system is running. Hard drives that can be hot-swapped cost significantly more than regular hard drives.

S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology)

You need to be aware of one more technology supported by both SSD and magnetic hard drives called S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology), which is used to predict when a drive is likely to fail. System UEFI/BIOS uses S.M.A.R.T. to monitor drive performance, temperature, and other factors.