tutor:Mass storage system
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A mass storage system may be thought of as an on-line automated tape library with capacities in excess of Terabytes. Also, it looks like a very fast huge, hard disk server. |
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Mass storage
Mass storage refers to the storage of large amounts of information in a persisting and machine-readable fashion. Storage media for mass storage include hard disks, floppy disks, flash memory, optical discs, magneto-optical discs, magnetic tape, drum memory, punched tape (mostly historic) and holographic memory (experimental). Mass storage includes devices with removable and non-removable media. It does not include random access memory (RAM), which is volatile in that it loses its contents after power loss.
Mass storage devices are characterized by:
- Sustainable transfer speed
- Seek time
- Cost
- Capacity
Component technologies of mass storage system
- Robotic storage libraries
- A system can hold many media units, disks or tapes, and use a robotic mechanism to load and unload drives. It offers automated access to data. Library capacities are huge and can be used in a networked computer environment.
- Storage media
- Newer storage technologies include helical scan magnetic tapes, and optical tapes. The storage densities, access speeds and costs for these new technologies are practical. Within a short time a terabyte size archive will be possible.
- Computer
- To efficiently feed high-performance fabricate CPUs, high capacity, high-speed I/O buses have been developed for mass storage system.
- Network
- High Performance Parallel Interface (HIPPI) standard allows data transfer speeds of up to one hundred megabytes per second. This leads to high storage devices being directly attached to networks.
- Storage management software
- Software controls the movement of data between storage devices, robotics, and networks.It also makes a large, fast, and flexible file system available.
Implication of mass storage system
Mass storage system usually implies a robotically controlled tape or disk library device or jukebox which is itself managed by a file server. Low-end systems are used to backup PC/workstation LANs, high-end mass storage systems have many applications including virtual disk, backup and archives. The media used for long-term storage include tapes and optical disks. Advantage of mass storage systems Robotic storage libraries or jukeboxes have been instrumental in bringing large volume to the single user and to the network. They have filled a gap that has existed between on-line storage and off-line or shelf storage.
Types of mass storage solutions
- Virtual disk
- A method of expanding the program-addressable online storage of a single computer. The well-known counterpart of virtual disk, virtual memory operates on the basic mechanism of a page fault and provides an indefinately large address space for programs executing in a host computer.
A virtual disk is useful for a single computer whose existing disk space is becoming exhausted and where it is uneconomical to keep adding more and more disks. With special software, this device can be used to transparently extend the local online disk space.
- Network file server
- A network file server supplies network users with large and cheap storage space. Some file servers use only magnetic disk; others use a storage hierarchy transparently managed by special software running on a control computer. The file server consists of fast-staging storage and large secondary, archive storage. Staging storage is online disk. It can be implemented through parallel disk arrays and software disk striping. Archive storage is usually implemented through tape, such as the IBM 3480.
Network file servers can be attached to more than one network. There are four categories of file servers:
- PC LANs ( local area networks; one to several gigabytes),
- workstation LANs (tens of gigabytes),
- departmental minis or minisupers ( a few hundred gigabytes), and
- large mainframes or supercomputers ( one to tens of terabytes)
In all cases, server is a shared network resource rather than being attached to one workstation or one computer because it provides cheap storage for many network users.
- The file server
- A file server is a repository in which data must be kept safely and indefinitely. For example, seismic data and earth observation data collection by satellites are generally kept in a file archive. The emphasis in a file archive is on low cost of storage and high reliability. The media used in a file archive must be stable over time, economical and reasonably fast.
The archives are implemented by the traditional tape library. This system can in many cases be replaced by devices and software which form a more effective new storage system.
- Automated network storage management
- The strategy used in this case is similar to the file server. A network file server is a large and fast device. because frequently accessed user files are cached on its fast disk. Infrequently used files are stored on tape. It has been shown that over 80% of the data in the system may be removed from expensive online storage without significantly sacrificing performance.
- Network file backup
- The backup problem has become particularly acute with the growing use of networked computing. With so many users on a network, it is impractical to require each one to be responsible for the backup of his data. Network-wide backup is considered a mass storage application simply because networks have so many users and the amount of data to backup is so large.
The use of common network resources, such as a computer server, a file server, suggests a common network-wide backup server. Applications for mass storage systems There are many applications for mass storage systems beyond the immediately obvious requirements for raw terabytes. Systems vendors need to be aware of the characteristics of mass storage to be able to identify valid uses for their products and demonstrate clear cost and functional advantages to prospective users.
Obvious applications for mass storage systems exist in many industries. Oil exploration, weather research, and the aerospace industry are a few examples. These industries all collect massive amounts of data, process them with high intensity for a short period of time, and then store them that they can be reused with as little delay as possible when needed.
Example of mass storage system
Phillips Business Systems has developed an electronic document storage and retrieval system called Megadoc, incorporating the digital optical recording (DOR) technology developed at Phillips Research Laboratories. Each side of a DOR optical disk has a Gigabyte capacity. The recording of redundant information enables Phillips to guarantee a ten-year life for each disk with a negligible information retrieval error rate of 1 bit undetected in 10^12 bits retrieved. Megadoc systems can be configured around jukeboxes of 64 disks, giving on-line access to 128 Gigabytes of information.
The technology has immense potential for many office archival applications. Its user-friendliness could be enhanced by the subsequent provision of such features as
- free text retrieval;
- high-speed scanning for specific groups of documents with keywords;
- speech input of indexing information;
- scanning of the text content ( in various fonts) of image documents
