14.113 Hard Disks, Sectors, Zone Bit Recording, Sectors vs Blocks, CHS, LBA, Sparing
Prof. Dr. Jens Dittrich, Big Data Analytics・2 minutes read
Hard disks are crucial for databases like IBM db2 and Oracle, as main memory technology is still slow to adopt. Large datasets in companies like Google and Yahoo cannot all fit in main memory, necessitating storage on hard disks with fast rotation speeds and fixed-size sectors for data access and recovery.
Insights
- Main memory technology adoption in major databases like IBM db2 and Oracle is slow, maintaining the relevance of hard disks due to their durability and ability to store large datasets that cannot fit entirely in main memory.
- The intricate design of hard disks, with platters, spindle, disk heads, and sectors, allows for efficient data read and write operations, with advancements in addressing from physical CHS to logical block addressing (LBA) enhancing data access and storage capabilities.
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Recent questions
Why are hard disks still relevant?
Hard disks remain relevant due to slow adoption of main memory technology in major database products like IBM db2 and Oracle, originally designed for disk-based systems.
Why is durability essential for databases?
Durability is crucial for databases as data needs to be persisted on a separate medium like hard disks or flash storage, as main memory data is lost during power failures.
How do large datasets like Google's fit in memory?
Large datasets, such as those in Google and Yahoo, cannot fit entirely in main memory, necessitating storage on hard disks.
What components make up a hard disk?
A hard disk consists of platters connected to a spindle, with magnetic platters that can be written to and read from using disk heads.
How do hard disks handle data access?
Hard disks have disk heads that move together on an arm, allowing access to different platters, but fine positioning is required for each track, preventing simultaneous use of all heads.
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Summary
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Relevance and Functionality of Hard Disks
- Hard disks are still relevant due to the slow adoption of main memory technology in major database products like IBM db2 and Oracle, which were originally designed for disk-based systems.
- Durability is essential for databases, requiring data to be persisted on a separate medium like hard disks or flash storage, as main memory data is lost during power failures.
- Large datasets, such as those in Google and Yahoo, cannot fit entirely in main memory, necessitating storage on hard disks.
- A hard disk consists of platters connected to a spindle, with magnetic platters that can be written to and read from using disk heads.
- Disk heads move together on an arm, allowing access to different platters, but fine positioning is required for each track, preventing simultaneous use of all heads.
- Virtual tracks and cylinders are defined by the arm's position and contain similar tracks across all platters.
- Hard disks rotate quickly, typically between 5,000 to 15,000 rotations per minute, with outer zones having higher transfer rates due to more sectors.
- Hard disk sectors are fixed-size units for read and write access, typically 4 kilobytes, and store self-correcting error codes for error detection and data recovery.
- Addressing data on hard disks evolved from physical CHS addressing to logical CHS addressing, and finally to logical block addressing (LBA), where sectors are only addressed by a logical block number mapped by the hard disk controller.
