Operating Systems Ch. 10 Mass-Storage Structure

Sector Sparing

Also known as forwarding, this uses more extra sectors to logically replace bad sectors.

Low-Level Formatting

Also known as physical formatting, this fills the disk with a special data for each sector.

Sector Slipping

An example of this is if logical block 17 becomes defective and the first available spare sector is 202. Then all the sectors in 17 are remapped to 202 moving them down all one spot. 202 to the spare, 201 to 202, 200 to 201 etc.

Host Controller

Data transfers on a bus are carried out by controllers. This controller is the one at the computer end of the bus.

Mean Time to Data Loss

Defined as: (Single disk's time to failure)^2 / (Total Disks)

Logical Blocks

Modern magnetic disk drives are addressed as large one-dimensional arrays of these, which is the smallest unit of transfer.

RAID

Redundant arrays of independent disks, This is used to helps prevent loss of data by using multiple disks in parallel to store redundant information.

Mean Time To Failure

The chance that some disk out of a set of N disks will fail is much higher than the chance that a specific single disk will fail. Defined as: (Single disk's time to failure) / (Total Disks)

Cylinder

The set of tracks that are at one arm position make up this.

Mirroring

The simplest (but most expensive) approach to redundancy is to duplicate every disk

Track

The surface of a platter is logically divided into circular these, which are then subdivided into sectors.

Rotational Latency

The time necessary for the desired sector to rotate to the disk head.

Seek Time

The time necessary to move the disk arm to the desired cylinder.

Magnetic Disk

These provide the bulk of secondary storage for modern computer systems.

FCFS Scheduling

This algorithm allows for the first disk in the queue to go first.

Data Striping

This consists of splitting the bits or blocks of each byte across multiple disks.

Disk Controller

This controller is built into each disk drive and is at the other end of the bus.

Solid-State Disk

This is a nonvolatile piece of memory that is used like a hard drive.

Storage-Area Network

This is a private network (using storage protocols rather than networking protocols) connecting servers and storage units.

C-SCAN Scheduling

This is a variant of SCAN designed to provide a more uniform wait time. Like SCAN, this moves the head from one end of the disk to the other servicing requests along the way.

Hot Spare

This is not used for data in RAID but is configured to be used as replacement in case of disk failure.

Transfer Rate

This is the rate at which data flow between the drive and the computer occurs.

Host-Attached Storage

This is the storage accessed through local I/O ports, and the ports use several technologies.

Sector

This is what tracks are subdivided into.

Disk Arm

This move all the heads as a single unit when reading from the platters on the disk.

Disk Scheduling

This process involves the following questions: Whether this operation is input or output? What the disk address for transfer is? What the memory address for the transfer is? What the number of sectors to be transferred is?

SSTF Scheduling

This selects the request with the least seek time from the current head position.

Redundancy (in RAID)

This stores extra information that is not normally needed but that can be used in the event of failure of a disk to rebuild the lost information.

Block-Level Striping

This type of data striping takes n disks, and puts a block i into one of the disks using (i mod n) + 1 formula

C-LOOK Scheduling

This type of scheduling is able to reverse data without going to the end, but must go back to the cylinder of the outermost request.

LOOK Scheduling

This type of scheduling is able to reverse data without going to the end, but will continue servicing once it reverses directions.

Network-Attached Storage

This type of storage is through a remote host in a distributed file system.

Bit-Level Striping

This version of striping data is uses bits.

Magnetic Tape

This was an early use of secondary-storage, it is relatively permanent and can hold large quantities of data, but its access time is slow compared with that of main memory and magnetic disk.

Platter

Each magnetic dis has one of these, which is a flat circular shape, like a CD. This is where information is stored magnetically.

SCAN Scheduling

In this algorithm the disk arm starts at one end of the disk and moves toward the other end, servicing requests as it reaches each cylinder, until it gets to the other end of the disk. Also known as elevator algorithm.