02-hard disk

02 -Hard Disk

?? Written by Zak Zhu

Reference

• Honghu Forum
• HCNA-Storage training materials V4.0

hard disk indicators

• Volume

  Hard disk capacity unit: GB

  The factors that affect the hard disk capacity are the capacity of a single disk and the number of disks

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• Rotational Speed

  The drive speed unit: RPM (Rotation Per Minute)

  Reach 5400RPM or 7200RPM

  SCSI interface hard disk speed can reach 10000 ~ 15000RPM

• Average Access Time

  Average access time = average seek time + average waiting time

• Data Transfer Rate

  Data transfer rate : Hard disk read and write data speed

  Unit: MB/s

  The hard disk data transfer rate includes two indicators: internal transfer rate and external transfer rate

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• Input/Output Per Second

  IOPS: Input and output per second, a key measurement for OLTP (OnLine Transaction Processing) applications Metrics

• Throughput

  Throughput: The amount of data that can be successfully transmitted per unit time, It is a key measurement indicator for OLAP (OnLine Analytical Processing) applications

hard disk type

disk principle

• The disc is covered by magnetic material, and the magnetic particles on the disc are polarized to represent a binary information unit
• Read/write head: responsible for reading and writing data:
  • Head Arm: Drive the read/write head, move the head to the specified position
  • Patter: Save the written data
  • Spindle: Rotate the platter, move the designated position on the platter to Under the read/write head
  • Control circuit: control the speed of the hard disk, the movement of the head arm, issue commands to the head, etc.
• The disk uses a fast The moving read/write head arm drives the magnetic head to read and write data from a flat disk coated with magnetic particles. The data is transferred from the disk platter to the computer through the read/write head.

Hard disk attributes

• A track is a concentric ring around the main shaft on the disc, and the data is recorded on the track. The track number starts from 0, starting from The outer edge of the platter begins to number inward. We use the number of tracks per inch (TPI) (also called track density) on the platter to measure the tightness of the tracks on the platter.
• Divided into smaller units, called sectors. A sector is the smallest storage unit in a disk that can be individually addressed. The track and sector structure are written on the platter by the hard disk manufacturer using the tool to format the hard disk. Different hard disk tracks The number of sectors can be different.
• Usually, a sector can store 512 bytes of user data
• Cylinder: All disks in the same disk (including upper and lower Two disks) with the same number of tracks form a cylinder, called the cylinder of the disk. The number of cylinders on the disk is the same as the number of tracks on a disk. The position of the head in the disk is indicated by the cylinder number. /li>

SAS disk

SAS provides an efficient, highly reliable, scalable and easy-to-operate solution for enterprise-level data centers. While SCSI is logically compatible, SAS provides unified support for SATA on the physical connection interface. This provides a lot of choice for applications such as servers and network storage.

NL-SAS disk

• NL SAS refers to the SATA disk with SAS interface and close to SAS performance.
• NL is the abbreviation of Near Line, which means near line. Nearline storage Mainly located in the application between online storage and offline storage. It refers to those data that are not frequently used, or that the data access is not large, placed on storage devices with lower performance. But at the same time, the requirements for these devices are Addressing quickly, The transmission rate is high. Therefore, near-line storage has relatively low performance requirements, but requires relatively good access performance. At the same time, in most cases, because infrequently used data account for a relatively large proportion of the total data volume, this is also It is required that nearline storage devices require relatively large capacity.

SSD disk

Overview of SSDs

• SSD principle:

  • Use Flash technology to store information

    SSD disks do not use magnetic materials to store data like traditional hard disks, but instead use cell (storage unit) NAND Flash to store data. NAND Flash is a non-volatile random access storage medium with its characteristics The data does not disappear after the power is off. This technology can quickly and compactly store digital information

  • There is no internal mechanical structure

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    The service life of SSD disks is limited. Since NAND Flash is a non-volatile medium, the block must be erased before writing new data, otherwise data errors may occur. But NAND Flash The number of erasing and writing is limited, that is, the number of times that the contents of each cell can be changed is limited. However, because this wear is easy to monitor and predict, we can prepare new hard disks for timely replacement. And mechanical hard disk failures are usually Without warning, this means that the replacement disk must be ready at any time

• Three main types of SSD:

  • Single Level Cell

    In SLC, each cell only stores 1 bit of data: 0 or 1

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  • Multi Level Cell

    In MLC, each cell can store 2bit data: 00, 01, 10 , 11

  • Triple Level Cell

    In TLC, each cell can store 3bit data: 000, 001, 010, 011, 100, 101, 110, 111

Solid State Disk Structure

SSD Performance advantages

• Short response time

The mechanical characteristics of traditional hard disks cause most of the time to be wasted on seeks and mechanical delays, and data transmission efficiency It is severely restricted. There are no mechanical moving parts inside the SSD hard disk, which eliminates seek time and mechanical delay, and can respond to read and write requests more quickly.

• Read High writing efficiency

  When the mechanical hard disk is performing random read and write operations, the magnetic head keeps moving, resulting in low read and write efficiency. The SSD uses the internal controller to calculate the data storage location and perform Reading and writing operations save mechanical operation time and greatly improve the efficiency of reading and writing.

Catalogue

• 02-Hard Disk
  • Reference
  • Hard Disk Index< /li>
  • Type of hard disk
  • Disk principle
  • Hard disk properties
  • SAS disk
  • NL-SAS disk
  • SSD disk