7th Week: CST 334

Hello everyone:

This week we covered CST 334 Topic: Persistence, which includes concepts such as I/O Devices, hard disk drives, RAID, files, directories, and file system implementation. I/O devices involve system architecture and methods to communicate with devices like polling, interrupts, and DMA to move data. Device drivers control the details of device communication so the operating system can focus on other tasks while the driver handles that part. Hard disk drives have been the primary form of persistent data storage in computers for a long time. Modern drives consist of sectors, which are blocks of memory typically 512 bytes each, that can be read or written individually. A disk is essentially an array of these sectors, ranging from zero to a maximum number, with each sector representing an addressable space. Updates to disk must be atomic.

RAID stands for Redundant Array of Inexpensive Disks that offers good reliability and performance by distributing data across multiple disks to make sure that data remains accessible even if one drive fails. Combining multiple disks allows for a faster, larger, and more reliable storage system. Files and directories are two key abstractions in persistent storage virtualization. A file is a sequence of bytes stored persistently and identified by its name and an OS-level identifier known as an inode number. A directory organizes files and subdirectories, storing their names and associated inode numbers. File systems use key structures like inodes for metadata, directories for name to inode mappings, and bitmaps to track free and allocated blocks. The design of file systems allows flexibility, giving optimizations and policy decisions. There was a lot of information to take in, and I realized I missed some details while reviewing. However, overall, I believe I understand the main points but I will revisit the material again.


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