数据库系统原理ch11.pptx

Chapter 11: Storage and File Structure;Chapter 11: Storage and File Structure;Classification of Physical Storage Media;Physical Storage Media;Physical Storage Media (Cont.);Physical Storage Media (Cont.);Physical Storage Media (Cont.);Physical Storage Media (Cont.);Storage Hierarchy;Storage Hierarchy (Cont.);Magnetic Hard Disk Mechanism;Magnetic Disks;Magnetic Disks (Cont.);Disk Subsystem;Performance Measures of Disks;Performance Measures (Cont.);Optimization of Disk-Block Access;Optimization of Disk Block Access (Cont.);Nonvolatile write buffers speed up disk writes by writing blocks to a non-volatile RAM buffer immediately Non-volatile RAM: battery backed up RAM or flash memory Even if power fails, the data is safe and will be written to disk when power returns Controller then writes to disk whenever the disk has no other requests or request has been pending for some time Database operations that require data to be safely stored before continuing can continue without waiting for data to be written to disk Writes can be reordered to minimize disk arm movement Log disk – a disk devoted to writing a sequential log of block updates Used exactly like nonvolatile RAM Write to log disk is very fast since no seeks are required No need for special hardware (NV-RAM) File systems typically reorder writes to disk to improve performance Journaling file systems write data in safe order to NV-RAM or log disk Reordering without journaling: risk of corruption of file system data;RAID;Improvement of Reliability via Redundancy;Improvement in Performance via Parallelism;RAID Levels;RAID Levels (Cont.);RAID Levels (Cont.);RAID Levels (Cont.);RAID Levels (Cont.);RAID Levels (Cont.);Choice of RAID Level;Choice of RAID Level (Cont.);Hardware Issues;Hardware Issues (Cont.);Optical Disks;Magnetic Tapes;Storage Access;Buffer Manager;Buffer-Replacement Policies;Buffer-Replacement Policies (Cont.);File Organization;Fixed-Length Records;Free Lists;Variable-Length Records;Variable-Length Rec