Select and install storage devices Flashcards
Mass storage device
Non-volatile storage devices hold data when the system is powered off. Mass storage devices use magnetic, optical, or solid-state technology to store data.
A mass storage device installed as an internal component is referred to as a fixed disk. standard widths: 5.25 inches, 3.5 inches, and 2.5 inches.
A fixed disk is typically installed to a drive bay using a caddy. You screw the drive into the caddy, then screw the caddy into the drive bay.
Factors mass storage device choice
Reliability—This concerns both the risk of total device failure and the risk of partial data corruption.
Performance —Along with the data throughput measured in MB/s or GB/s, you may need to consider the number of input/output operations per second (IOPS) that can be achieved by a device for different kinds of data transfer operations.
Use—Reliability and performance factors can only be properly evaluated when considering use. Examples of how storage is used include running an OS, hosting a database application, streaming audio/video data, as removable media, and for data backup and archiving.
Solid-state drives
A solid-state drive (SSD) uses flash memory technology to implement persistent mass storage. Flash memory performs much better than the mechanical components used in hard disk drives, especially in terms of read performance.
Flash chips are also susceptible to a type of degradation over the course of many write operations.
SSD Communications Interface
SSD might be packaged in a 2.5-inch caddy and installed to a SATA port using the normal SATA data and power connectors. Alternatively, the mSATA form factor allows an SSD packaged as an adapter card to be plugged into a combined data and power port on the motherboard. With both form factors, the main drawback is that the 600 MBps SATA interface can be a bottleneck to the best performing SSDs, which can achieve transfer rates of up to 6.7 GB/s.
modern SSDs often use the PCI Express (PCIe) bus directly. Where SATA uses the advanced host controller interface (AHCI) logical interface to communicate with the bus, PCIe-based SSDs use the non-volatile memory host controller interface specification (NVMHCI) or NVM Express (NVMe) .
An NVMe SSD can either be packaged for installation to a PCIe slot as an expansion card or to an M.2 slot.
Hard Disk Drives
A hard disk drive (HDD) stores data on metal or glass platters that are coated with a magnetic substance. The top and bottom of each platter is accessed by its own read/write head, moved by an actuator mechanism. The platters are mounted on a spindle and spun at high speed. Each side of each platter is divided into circular tracks, and a track contains several sectors, each with a capacity of 512 bytes.
High performance drives are rated at 15,000 or 10,000 rpm; average performance is 7,200 or 5,400 rpm. A high-performance drive will have an access time below 3 ms; a typical drive might have an access time of around 6 ms.
Most HDDs use a SATA interface, though you may come across legacy devices using EIDE/PATA or SCSI interfaces.
PCs are 3.5-inch units. The 2.5 -inch form factor is used for laptops and as portable external drives. 2.5-inch form factors can also vary in height, with 15 mm, 9.5 mm, 7 mm, and 5 mm form factors available.
Redundant Array of Independent Disks
To mitigate these risks, the disks that underpin the mass storage system can be provisioned as a redundant array of independent disks (RAID) . Redundancy sacrifices some disk capacity but provides fault tolerance. To the OS, the RAID array appears as a single storage resource, or volume, and can be partitioned and formatted like any other drive.
A RAID level represents a drive configuration with a given type of fault tolerance. Basic RAID levels are numbered from 0 to 6. There are also nested RAID solutions, such as RAID 10 (RAID 1 + RAID 0).
RAID can be implemented using features of the operating system, referred to as software RAID. Hardware RAID uses a dedicated controller, installed as an adapter card. The RAID disks are connected to SATA ports on the RAID controller adapter card, rather than to the motherboard, hardware RAID is often able to hot swap a damaged disk. Hot swap means that the failed device can be replaced without shutting down the operating system.
RAID 0
Disk striping divides data into blocks and spreads the blocks in a fixed order among all the disks in the array. This improves performance as multiple disks are available to service requests in parallel. RAID 0 requires at least two disks. RAID 0 provides no redundancy at all.
RAID 1
RAID 1 is a mirrored drive configuration using two disks. Each write operation is duplicated on the second disk in the set, introducing a small performance overhead.
This strategy is the simplest way of protecting a single disk against failure. If one disk fails, the other takes over. When the disk is replaced, it must be populated with data from the other disk. In terms of cost per gigabyte, disk mirroring is more expensive than other forms of fault tolerance because disk space utilization is only 50%.
RAID 5
RAID 5 uses striping (like RAID 0) but with distributed parity. Distributed parity means that error correction information is spread across all the disks in the array.
If a single disk fails, enough information is spread across the remaining disks to allow the data to be reconstructed. RAID 5 requires a minimum of three drives but can be configured with more.
The level of fault tolerance and available disk space is inverse. As you add disks to the set, fault tolerance decreases but usable disk space increases. Using a three 80 GB disk configuration, you would have a 160 GB usable volume. If four are used, one-quarter is reserved on each disk. Using a four 80 GB disk configuration, you would have a 240 GB usable volume.
RAID 10
RAID 10 is a logical striped volume (RAID 0) configured with two mirrored arrays (RAID 1). This configuration offers excellent fault tolerance, as one disk in each mirror can fail, and the volume will still be available.
This configuration requires at least four disks, and there must be an even number of disks. It carries the same 50% disk overhead as mirroring.
Removable Storage Drives
Removable storage can refer either to a storage device that can be moved from computer to computer without having to open the case or to storage media that is removable from its drive.
Drive Enclosures
HDDs and SSDs can be provisioned as removable storage in an enclosure. The enclosure provides a data interface (USB, Thunderbolt, or eSATA), a power connector (if necessary), and protection for the disk.
Some enclosures can be connected directly to a network rather than to a PC. This is referred to as network attached storage (NAS). Advanced enclosures can host multiple disk units configured as a RAID array.
A flash drive —also called a USB drive, thumb drive, or pen drive—is simply a flash memory board with a USB connector and protective cover.
The memory card form factor is used in consumer digital imaging products, such as digital still and video cameras, and to expand smartphone and tablet storage.
Optical Drives
Compact Discs (CDs), Digital Versatile Discs (DVDs), and Blu-ray Discs (BDs) are mainstream storage formats for music and video retail. All types of optical media use a laser to read the data encoded on the disc surface.
CD has a maximum capacity of 700 MB and is available in recordable (CD-R) and rewritable (CD-RW) formats. The base transfer rate of a CD is 150 KBps.
DVD has a capacity of 4.7 GB for a single layer, single-sided disc up to about 17 GB for a dual-layer, double-sided disc.The base transfer rate for DVD is 1.32 MBps, equivalent to 9x CD speed.
Blu-ray has a capacity of 25 GB per layer. The base speed for Blu-ray is 4.5 MBps, and the maximum theoretical rate is 16x (72 MBps).
An internal optical drive can be installed to a 5.25-inch drive bay and connected to the motherboard via SATA data and power connectors.
