Unit 5 - Storage
JBOD
- "just a bunch of disks" - Not a RAID configuration - creates a single volume using space from two or more disks
Benefits of RAID
- can improve performance - can provide fault tolerance
SCSI uses and advantages
- connects multiple devices onto a single bus or chain. - provides better performance than PATA or SATA. - relatively difficult to configure - devices must be configured with a device ID, and the bus must be terminated - more expensive than PATA/SATA. - most commonly used for tape storage devices and hard disks - can also be used for devices such as CD-ROM drives, scanners, and printers.
Advantages SATA
- most commonly used hard disk interface - 150MBs - 600MBs - faster than PATA. - built-in support for disk protection methods - easy configuration--just connect the device to the SATA port. - supports external devices as well - capable of hot swapping
ISO9660
-A more standardized format than the original CD-ROM standard. Unlike other standards based on the original CD-ROM standard, this standard is not operating system- specific. The predecessor to the ISO 9660 standard was called the High Sierra format.
CD-ROM
-The original data CD standard. Several variations of the original data CD-ROM standard exist, but they are largely specific to particular operating systems.
SCSI 1
1986 bus width: 8-bits bus speed: 5MHz Lack of Compatibility up to 8 Devices
SCSI 2
1990 goal: standardize standard connectors standard bus widths (8-bit or 16-bit "wide") standard bus speeds (5MHz bus, 10MHz bus "fast") up to 8 Devices
How to determine Optical Drive Speed
1x = 150KB/s Read Speed Write x Read Write x Rewrite x Read
BlueRay Speed
1x = 4.5 Mbps 2x = 9 Mbps (minimum needed for HD content)
Differential
2 wires per data bit Max 25 Meters
Advantage of Striping
2 x speed
DVD
4.7 GB or over 2 hours
DVD - RW
4.7GB Storage Photo reactive crystalline coating write laser causes crystal to form to create a land Playable in most DVD drives and players
DVD ROM
4.7GB Storage Read Only Memory Rated according to Speed 1x - 11 Mbps 2x - 22Mbs
DVD-R Also, DVD-RG/DVD-RA
4.7GB Storage Recordable - Write Once/Read Many Bottom coated with organic dye Laser creates dark spot or "pit" Most compatible with DVD players
Original CD specifications
74minutes audio (later went up to 80min) 650 - 680 MB 120mm diameter, 1.2mm thick Pits and Lands
Dual Layer DVD
9.4 GB
Disadvantage of Striping
A failure of one disk in the set means all data is lost. Does not provide fault tolerance.
Hard disk
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.
Solid state drives
A solid state drive is a flash device with a storage capacity similar to a small hard drive.
CD-ROM XA
An extension to the ISO 9660 standard. Allows multiple types of data (audio, data, video) to be put on the same CD.
Red
Audio CDs: CD-DA
Striping
Breaks data into units and stores the units across a series of disks by reading and writing to all disks simultaneously. Requires a minimum of two disks.
Which has more room for write or read error, DVD or CD?
CD
3 Types of CDs for computers
CDRom, CDR, CDRW
Disc Drives have to be formatted to country
Can only be reformatted 5 times
Common flash devices include:
Compact Flash cards MMC cards SD cards SDHC cards Mini-SD cards Micro-SD cards XD cards Memory sticks USB thumb drives.
Yellow
Data CDs CD-ROM ISO 9660 CD-ROM XA
Some disadvantages of tape drives
Data must be read from tape sequentially. The tape must be cued to the exact location on tape when data must be retrieved. Access to data is slower Wear Out over time if rewritten to repeatedly
CD-DA
Digital Audio
Disadvantage of Mirroring
Does not increase performance. 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.
USB/Firewire
External Device connections
Some of the advantages of flash devices are:
Extremely portable Re-programmable Retain content without power Extremely small Optimal for use in devices like cameras Larger capacity than CDs and DVDs Relatively fast memory access
Some advantages of solid state drives:
Faster than hard drives No moving parts so they last longer Less Heat due to no moving parts Lower power consumption than hard drives (good for laptops) They are less susceptible to physical damage (from dropping) and immune from magnetic fields Smaller and lighter than hard drives
Flash devices
Flash devices store information using programmable, non-volatile flash memory.
Examples of removable media
Floppy Disks Optical Discs Flash Devices eSATA drives Tapes
Not Removable media
Hard Disks Solid State Drives - installed internally in the computer.
BlueRay Disk (BD)
High Definition Color of the laser is different CD/DVD uses RED laser BD uses BLUE laser (tighter wavelength) Single Layer = 25GB Double Layer = 50GB 20 Layer = 500GB BD-ROM, BD-R, BD-RE
Green
Interactive CDs CD-I
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 (i.e. when dropped)
Some disadvantages of PATA interfaces:
Maximum speed of 133 MB/s. Because both devices share the same channel, devices must be configured properly to avoid conflicts. Not Capable of Hot Swapping devices They are being phased out and replaced.
RAID 1 Array
Mirroring
Duplexing
Mirroring using 2 RAID controllers, one for each drive
Orange
Multi-session CDs CD-R- CD-RW-
Pits
Non reflective
Optical discs
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.
DVD Video
Over 2 hours different aspect ratios 8 different audio tracks 32 subtitle tracks
PATA
Parallel ATA
Distributed Parity
Parity Information is stored on and distributed across a section of all three disks
Advantage of Mirroring
Provides fault tolerance for a single disk failure. Increased redundancy
RAID
Redundant Array of Independent Disks - combines multiple physical disks into a single logical storage unit
4 Standards of SCSI 2 (bus width/speed)
Regular 8-bit 5MHz Wide 16-bit 5MHz Fast 8-bit 10MHz Wide-Fast 16-bit 10MHz
CD/DVD drive interfaces
SATA or External USB
DVD+ R DVD+RW
Same as -R versions More Robust
SATA
Serial ATA
SCSI 2 Signaling
Single Ended Differential (not compatible with each other but no difference in the plug)
SCSI
Small Computer System Interface
Some of the disadvantages of floppy disks are:
Small capacity (1.4 MB) Slow They are magnetic Obsolete
Some of the disadvantages of flash devices are:
Storage Capacity is smaller than Hard Disk Drives and Solid State Drives Different memory card formats require different readers
Mirroring
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. Requires two disks.
RAID 0 Array
Striping
Typed of RAID Arrays
Striping Mirroring Parity
RAID 5 Array
Striping with distributed parity (min. of 3 disks)
Parity
Striping with increased Redundancy - add additional disk to mirrored RAID that contains "parity information"
Tape drives
Tape drives (also called digital linear tape or DLT drives) store data on magnetic tapes, similar to audio cassette tapes. Tape drives are most commonly used for data backups, such as taking a backup of all hard drives in a system.
Some advantages of tape drives:
Tapes can typically store large amounts of data. DLT tapes range in capacity from 10 GB to 800 GB per tape. Tapes can be changed, allowing you to save data from different sources on the same drive. Tapes are relatively inexpensive and small enough for long-term storage.
CD-RW
The standard for re-writeable optical CDs - Photo reactive crystalline coating - write laser causes crystal to form to create a land
CD-R
The standard for recordable optical CDs - Photo reactive dye on bottom - write laser changes pigment to create a pit
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
Some of the advantages of floppy disks are:
They are portable At one time, they were universally implemented Can be used as a boot device
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 They can get scratched if not protected
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
SCSI 3 Cables
Ultra = Single Ended or Differential 1.5M 25M Wide Ultra & Ultra 2 = Differential only 25M Ultra 3 = Differential only 12M
4 Standards of SCSI 3 (bus width/speed)
Ultra SCSI 20MHz/8-Bit Wide Ultra SCSI 20MHz/16Bit Ultra 2 SCSI 40MHz/8Bit Wide Ultra 2 SCSI 40MHz/16Bit Ultra 3 SCSI 80MHz/8Bit Wide Ultra 3 SCSI 80MHz/16Bit
White
Video CDs--A standard for structuring digitized MPEG video files.
Ethernet
You can connect hard disks directly to your Ethernet network using Network Attached Storage (NAS). The NAS device includes a built-in file server, allowing multiple network users to attach to and use the storage within the device.
Serial ATA (SATA)
a computer bus technology primarily designed for transfer of data from a hard disk which uses serial communication (meaning each device is on its own channel) - the successor to PATA
Floppy disk
a single, flexible disk covered with a magnetic film that is a little thicker than paper. The disk is protected by a thin outer sleeve. A read head spins the floppy to take information from the read hole in the center of the floppy.
Small Computer System Interface (SCSI)
a standard for transferring data between devices on internal and external computer buses, typically used in servers that have high availability and speed requirements.
Compact Disc formats are categorized by
book color: Red, Yellow, Green, White, Orange
Blu-ray discs
can store a large amount of data (25 GB or more, depending upon the format)
Parallel ATA (PATA)
computer bus technology primarily designed for transfer of data from hard disk drives and CD-ROM drives which uses parallel communication (meaning devices share the same data transfer channel) - when one device needs to send data the other device will not be able to send data until the first device is finished.
A hard drive enclosure allows you to
connect a PATA or SATA hard drive to the USB or Firewire port of your computer, making the hard drives a form of portable storage.
Serial SATA Supports external devices through
eSATA
Removable storage devices are typically connected through
eSATA, USB, or Firewire ports
Spanning
is another term for JBOD because the volume spans multiple physical disks. (data is typically saved to the first disk until it is full, then additional data is saved to the second disk and so on.) - disks can be different sizes - no performance or fault tolerance benefits
The main disadvantage currently for solid state drives
is cost--they are several times more expensive than comparable hard drives
Single Ended
most widely implemented version 1 wire per data bit Max 6 Meters
For all RAID configurations, the amount of disk space used on each disk must be what size?
of equal size
CD-i
playback audio and video (obsolete)
Lands
reflective
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).
If disks in the array are of different sizes, what happens?
the resulting volume will be limited to the smallest disk.
SCSI 3
up to 16 Devices standard bus widths (8-bit or 16-bit "wide") - no change standard bus speeds (20MHz bus "ultra SCSI" , 40MHz bus "ultra 2 SCSI", 80MHz bus "ultra 3 SCSI" )
