Storage Flashcards
Hard Disk Drive (HDD)
A hard disk is a thick magnetic disk encased in a thicker protective shell. A hard disk consists of several aluminum platters, each of which requires a read/write head for each side. All of the read/write heads are attached to a single access arm to prevent them from moving independently. Each platter has circular tracks that cut through all of the platters in the drive to form cylinders. The spinning of the platters is referred to as revolutions per minute (RPM). The higher the revolutions per minute, the faster the data can be accessed. Standard hard drives are categorized as follow:
- 5400 rpm (inexpensive HDD)
- 7200 rpm (good quality HDD)
- 10,000 rpm (expensive HDD)
Some of the advantages of hard disks are:
- They have lots of storage (starting at 16 GB up to several TB).
- They are significantly faster than floppy disks.
- The cost per MB is cheap.
Some of the disadvantages of hard disks are:
- Many hard disks are internal devices, though you can get external enclosures.
- They are prone to failure.
- They are vulnerable to physical damage (e.g., when dropped).
SCSI is a standard for transferring data between devices on internal and external computer buses. Though SCSI devices are most commonly used for tape storage devices and hard disks, they can also be used for devices such as CD-ROM drives, scanners, and printers.
Non-Volatile Memory Express (NVMe)
A memory storage device designed to allow access to non-volatile storage media through a PCI express (PCIe) bus.
NVM Express is designed to work well with low latency and internal parallelism of solid-state storage devices. By allowing host hardware and software to utilize the level of parallelism possible in modern SSDs, NVM Express reduces I/O overhead and improves functionality.
NVM Express devices come in three forms. The most common are standard-sized PCI Express expansion cards and a 2.5-inch form-factor devices that provide a four-lane PCI Express interface through the U.2 connector. There are also storage devices that use SATA Express and the M.2 specification, which support NVM Express as the logical device interface.
Flash Devices
Flash memory cards store information using programmable, non-volatile flash memory. Some of the advantages of flash devices are:
- The memory is re-programmable.
- They can retain content without power.
- They are optimal for use in devices like cameras.
- They are highly portable.
- They have a larger capacity than CDs and DVDs.
- They have relatively fast memory access.
Some of the disadvantages of flash devices are:
- Their storage capacity is not yet comparable to the capacity of modern hard disks.
- Different memory card formats require different readers.
Common flash memory cards include:
- CompactFlash cards
- SD cards
- SSD cards
- MiniSD cards
- MicroSD cards
- xD cards
- Hybrid cards (combines SSD and HDD technology)
- Memory sticks
Optical Disc
Optical discs such as CDs, DVDs, and Blu-ray discs are a storage medium that uses lasers for both reading and writing information. Optical discs store information through pits in their reflective coating. As the disc spins, the optical drive sends laser optics to the disk and receives the stored information through the deflected output.
Some of the advantages of optical discs are:
- They are great for music and video (they play in audio or video devices that aren’t computers).
- They are portable and universal.
- They are cheap.
- You can buy discs that are recordable.
- They have a long shelf life and are relatively sturdy.
- Blu-ray discs can store a large amount of data (25 GB or more, depending upon the format).
Some of the disadvantages of optical discs are:
- They are slower than hard disks.
- They have a small capacity (650 MB for CDs, 4.7 GB for DVDs).
- There are some compatibility issues between disc formats and readers
Solid State Drive (SSD)
A solid state drive is a flash device with a storage capacity similar to a small hard drive. Solid state drives are used as replacements for hard disk drives for storing operating system, application, and data files.
Some advantages of solid state drives:
- They are faster than hard drives.
- They have no moving parts.
- They have lower power consumption than hard drives (good for laptops).
- They are less susceptible to physical damage (from dropping) and immune from magnetic fields.
- They are smaller and lighter than hard drives
The main disadvantage currently for solid state drives is cost. They are several times more expensive than comparable hard drives. However, their advantages make them a good choice, especially for portable devices. M.2 is a popular SSD for portable devices
Integrated Drive Electronics (IDE)
An electronic interface allows communication between a motherboard’s data paths or bus and a computer’s hard disks.
Removable storage
Removable storage refers to the ability to easily connect and disconnect storage devices or storage media from a computer (as compared to internal or fixed storage). Optical discs, flash devices, eSATA drives, and tapes are examples of removable media. Hard disks and solid state drives are typically not removable media as they are installed internally in the computer.
Serial ATA (SATA)
Serial ATA (SATA) is computer bus technology primarily designed for the transfer of data from a hard disk. SATA:
- Uses serial communication (meaning each device is on its own channel).
- Provides built-in support for disk protection methods.
- Provides for easy configuration. Just connect the device to the SATA port.
- Has an L-shaped connector.
- Supports external devices through the external SATA (also called eSATA) standard. eSATA is faster than USB
Be familiar with the following SATA standards
Standard
Description
SATA1
SATA1 is the original SATA standard. It provided for 1.5 Gbps (150 MBps) data transfer.
SATA2
The second generation of SATA devices support up to 3 Gbps (300 MBps). SATA2 includes the following enhancements:
- Xbox360 hard disk interface (called xSATA)
- Hot pluggable support, allowing drives to be added and removed while the system is running
- Improved connectors to reduce ESD, improved usability, and extended life when used with external devices
- Native Command Queuing (NCQ) for increased performance
- Port multiplier support, allowing multiple devices to be connected to a single SATA port
SATA3
The third generation of SATA devices support up to 6 Gbps (600 MBps).
- This standard mainly addresses solid state drives with SATA (hard disk drives are not capable with sending data at this rate).
- The standard includes new connectors for solid state devices and thin optical drives.
eSATA
The eSATA (external SATA) standards are a subset of other standards specifically for externally connected devices.
- eSATA devices use a special SATA data cable with a locking clip to prevent the cable from being accidently disconnected.
- Because power is not supplied through the SATA data cable, eSATA devices require an external power connector or power source.
- eSATA is typically faster than USB.
- eSATA has a rectangular connector.
eSATAp
The eSATAp (Power over eSATA or Power eSATA) standards are meant to replace eSATA.
- eSATAp combines the functionality of an eSATA and a USB port with a source of power in a single connector.
- Both SATA data and device power are integrated in a single cable.
- The eSATAp connector and port are neither an L-shaped or rectangular.
Facts about SATA
- Each SATA drive has its own channel, with a single drive connected to each cable and port.
- The cable length can be up to one meter (up to 2 meters for eSATA).
- SATA devices use a special 15-pin power connector that supplies 3.3, 5, and 12 volts. You can use an adapter cable to convert a 4-pin Molex connector to a SATA power connector, but if you do, the resulting cable will not have 3.3 volts (3.3 volts are typically not used in most SATA devices).
- Devices you can connect using SATA include:
- Hard disk drives (HDD)
- Optical drives (CD/DVD/Blu-ray)
- Solid state drives (SSD)
- All new motherboards include support for multiple SATA devices.
- Some motherboards include eSATA connectors, or you can use a port connector device to add external ports using the internal SATA connections.
- You can also install an adapter card in an available bus slot to increase the number of SATA ports.
- Removable storage devices are typically connected through eSATA or USB. A hard drive enclosure allows you to connect a SATA hard drive to the USB port of your computer, making the hard drive a form of portable storage.
- Connect the boot drive to the lowest SATA channel number of the installed devices. The boot sequence will normally follow the channel order unless a boot priority is specified in the BIOS/UEFI.
- When installing a newer SATA2 drive into a system that supports only SATA1, you might need to:
- Configure the drive to operate in SATA1 mode. This is typically done by setting a jumper.
- Update the BIOS/UEFI to recognize the new drive.
Even with these steps, some SATA2 drives will not work in a motherboard that supports only SATA1. In that case, install a SATA2 controller card.
- eSATA cards offer simple connectivity between a host computer and eSATA devices. And remember that you also have the option to use expansion cards as needed
DVD (Digital Video Disc or Digital Versatile Disc)
DVD (Digital Video Disc or Digital Versatile Disc) is an optical media standard that can be used to store large amounts of different types of data (computer data, video, audio).
Compact Disc (CD)
CDs were first developed to store digital music. Later, the CD technology was adapted to store digital computer data. A CD:
- Can hold 74 to 80 minutes of audio
- Is 120 millimeters in diameter
- Is 1.2 millimeters thick
CD-ROM stands for compact disc read-only memory. CD-ROMs are identical in appearance to audio CDs, and data is stored and retrieved in a very similar manner. CD-ROMs:
- Have lands and pits and use reflective light to interpret the data on the disc.
- Hold about 737 MB of data with error correction or 847 MB total.
- Transfers data at a rate of 150 KBps.
- Drive speeds are measured as multiples of this original speed. To calculate an estimate of your CD-ROM drives transfer rate, multiply its speed by 150 kilobyte (1x = 150 KBps, 2x drive = 300 KBps, 4x drive = 600 KBps, 72x = 10,800 KBps).
CD-RW stands for Compact Disc-ReWritable.
- CD-RW can be written, read many times, erased, and rewritten.
- CD-RW has a capacity of about 650 MB.
- CD-RW is a removable hard drive, because you can insert the disc into the disc drive on one PC, add and delete data, eject it, and insert it into another disc drive on another system and have all your data immediately accessible.
- CD-RW drives can burn or write to CD-RW discs, erase CD-RW discs, and read a CD-ROM disc.
- CD-RW drive speed rating includes three parameters: a write speed, a rewrite speed, and a CD-RW read speed. All of these are multiples of the original 150 KBps 1x speed defined by the first CD-ROM drives. For example, if you have an 8x4x32 CD-RW drive, this means that it can write at 1,200 KBps, it can rewrite to a CD-RW disk at 600 KBps, and it can read at 4,800 KBps.
- The bottom surface of a CD-RW drive is coated with a photo reactive crystalline coating. A red laser causes a crystal to form which creates the reflective and non-reflective areas on the bottom of the CD-RW disc.
- A CD-RW drive has a second, high power write laser. When this laser hits the bottom of this photo reactive material on the bottom of the CD-RW disc, it causes crystals to form. This is called phase shifting or a phase shifting media. A crystal forming on the bottom of a CD-RW disc is like a land on a CD-ROM disk, because it reflects light.
Digital Versatile Disc (DVD)
DVD (Digital Versatile Disc) is an optical media standard that can be used to store large amounts of different types of data (computer data, video, audio).
- Most DVD drives can read and write. Older drives or older DVD players might only support DVD-R.
- A DVD with a single side of data can hold about 4.7 GB.
- A DVD-ROM is read-only memory.
- DVD-RW is a rewritable DVD format.
- DVD-RW uses a crystal encoding on the bottom of the DVD disc.
- A DVD-RW DL employs two recordable dye layers, each capable of storing about 4.7 GB; the total disk capacity is 8.5 GB.
- Some DVDs can store data in two different layers on the same side.
- The outer layer is semi-transparent, allowing the laser to read data from the inner layer.
- Dual-layer discs can hold up to 8.5 GB of data.
- Dual-layer recordable discs cost more than single layer discs.
- Dual-layer DVDs are recorded using Opposite Track Path (OTP).
- Most newer drives can read both single and dual layer discs. However, older drives might not support dual layer discs.
- DVD speeds use a multiple of 1.35 MBps (1x = 1.35 MBps, 2x = 2.7 MBps, etc.) or 11 Mbps (1x = 11 Mbps, 2x = 22 Mbps, etc.).
Blu-ray Disc (BD)
Blu-ray Disc (BD) is a newer optical disc format that is capable of greater storage capacity than DVDs.
- Blu-ray was originally developed for high definition video (and expanded content on movie discs), but can also be used for data storage.
- Blu-ray uses a blue laser instead of the red laser used with CDs and DVDs. The blue laser light has a shorter wavelength, which allows data to be packed more tightly on the disc.
- A single layer Blu-ray disc holds 25 GB; a double layer disc holds up to 50 GB. Experimental 20 layer discs can hold up to 500 GB.
- Blu-ray discs can be read-only (BD-ROM), recordable (BD-R), or rewritable (BD-RE).
- A 1x Blu-ray drive reads data at 4.5 MBps.
- Most Blu-ray drives include a second read laser for reading CDs and DVDs. Without this additional laser, Blu-ray drives would not be able to read CDs or DVDs.
- Blu-ray is intended to eventually replace DVD.
- Blu-ray has become the accepted HD video standard as the last movie studio stopped distributing HD DVD movies
Be aware of the following when working with optical drives
- When you place a disc in the drive, it can take several seconds for the drive to recognize the new disc and spin up to speed. If you receive a message saying that the drive is not accessible after trying to access a recently inserted new disc, wait a few seconds and try again..
- If you install a new hard drive, the drive letter for your optical drive might change. Software programs or shortcuts that rely on the old drive letter will likely not run properly until they have been told the correct drive letter for the drive.
- Access time is a general measure of drive performance. Like hard drives, average access time includes average seek time and average latency time. However, it also includes average spin up/down time. This is the time required for a drive to spin up or down to the proper speed to read the data from that particular location of the disc.
- If the drive tray won’t open for some reason, you can insert a straightened paper clip in the small hole beneath the drive door to push the drive tray out of the drive
Precautions to protect discs
- Some recordable discs use a foil placed on the top of the disc instead of imbedding the foil inside the plastic. Be very careful when working with these types of discs. A scratch or even some types of markers can damage this layer..
- To help prevent scratching, keep the disc in its case when not being used.
- To minimize the effect of scratches that might be generated while wiping a disc, wipe the disc in straight lines from the center to the edge (like the spokes of a wheel).
- Keep the disc away from direct sunlight and other sources of heat.
Redundant Array of Independent Disks (RAID)
Redundant Array of Independent Disks (RAID), also called Redundant Array of Inexpensive Disks, is a disk subsystem that combines multiple physical disks into a single logical storage unit. Depending on the configuration, a RAID array can improve performance, provide fault tolerance, or both.
RAID 0 (Striping)
A stripe set breaks data into units and stores the units across a series of disks by reading and writing to all disks simultaneously. Striping:
- Provides an increase in performance.
- Does not provide fault tolerance. A failure of one disk in the set means all data is lost.
- Requires a minimum of two disks.
- Has no overhead because all disk space is available for storing data.
RAID 1 (Mirroring)
A mirrored volume stores data to two duplicate disks simultaneously. If one disk fails, data is present on the other disk, and the system switches immediately from the failed disk to the functioning disk. Mirroring:
- Provides fault tolerance for a single disk failure.
- Does not increase performance.
- Requires two disks.
- Has a 50% overhead. Data is written twice, meaning that half of the disk space is used to store the second copy of the data. Overhead is 1 / n where n is the price of the second disk.
- RAID 1 is the most expensive fault tolerant system.
