C191 - Chapter 9 (Mass Storage Structure)

Spindle
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Terms in this set (40)
Spindle
Pole that rotates in a hard drive
Disk Arm
What the drive heads are attached to that moves the heads as a unit.
Tracks
The circular divisions of a disk platter
Sectors
The divisions of a track on a platter in a hard drive. This is the lowest level of division that stores the data.
Cylinder
The set of tracks that are at ONE arm position.
Transfer Rate
The rate at which data flows from the drive to the computer.
Positioning Time (Random-Access-Time)
Consists of 2 parts, the "Seek Time" and the "Rotational Latency".
Seek Time
The time it takes to move the arm to the desired cylinder.
Rotational Latency
Time for the sector to rotate to the disk head on the arm
Head Crash
When the head hits the platter and damage has occurred.
Disk ControllerBuilt in to each disk drive and carries out the command pass to it from the host controllerHost ControllerThe controller at the computer end of the busI/O BusA disk drive attached to the computer by a set of cables.ControllersElectronic processors that carry out data transfers on a busSSDSolid-State Drives (No moving parts)Logical BlocksThe smallest unit of transfers, usually 512 bytes. Mapped to the sectors sequentially starting at sector 0 and moving out to in on the cylinderConstant Linear Velocity (CLV)Density of tracks are uniform, so the tracks farther from the center of the disk, the greater the length, so it can hold more sectors. So drive increases with speed as the heads move closer to the centerConstant Angular VelocityDisk rotation speed stays constant and the density of the bits decrease from inner tracks to outer tracks to keep data rate constant.Host-Attached StorageAccessed via local I/O PortsNetwork-Attached StorageAccessed via a remote hostiSCSINAS Protocol. Uses IP Protocol to carry SCSI Protocol.Disk BandwidthThe total number of bytes transferred, divided by the total time between the first request and the completion of the last transferFCFSFirst Come First Serve Scheduling. does not provide fastest serviceSSTFShortest Seek Time First: - All requests that are closed to the head are serviced first. - Essentially it is "SJF" (Shortest Job First). - May Cause Starvation - Better than FCFS, but not optimalSCANDisk arm starts at one end of the disk and moves towards the other end, then reverses. - Referred as the "Elevator Algorithm"C-SCANCircular SCAN: Acts just like SCAN, but instead of servicing requests on the way back, it moves back to the start and then starts servicing requests from the beginning again.LOOK/C-LOOKSame as both SCAN/C-SCAN, but instead of moving the head all the way to the edges of the platter, it stops and reverses at the farthest requests for services.Header/TrailerContains info on sector number and ECC (Error Correcting Code)Logical FormattingThe creation of the File SystemClustersLarge groups of blocks made by File Systems. - Disk I/O is done via blocks - File System I/O is done via clustersPartitionBreaking the disk up by Cylinders. Each Cylinder (Partition) can be treated as if it was a separate disk.Sector Sparing / ForwardingA controller thats told to replace each bad sector "logically" with one of its spare sectors.Swap-Space ManagementVirtual Memory uses disk space as an extension of main memory. -Swap space is only used as a backing store for pages of ANONYMOUS memory. -Decreases system performance -Low level task of OSSwap Mapan array of integers that corresponds to the # of mappings to the swapped page.RAID 0Striping - no redundancyRAID 1Mirroring