File management

File Systems Architecture device drivers physical I/O (PIOCS) logical I/O (LIOCS) access methods File organization and access l sequential l index-sequential l direct

File sharing and blocking n File sharing – access rights: read, write, execute, by user classes. – File/record locking: simultaneous access n Record blocking – Logical vs physical record – unblocked vs blocked record – fixed-length vs variable-length IRG block data IBG block data IBG IRG

File allocation n File allocation table (FAT) n Pre allocation vs dynamic allocation n Portion size – contiguity increases performance – fixed-size portions simplify reallocation – variable-size or small fixed-size minimizes waste of unused space for overallocation – two main alternatives: l variable, large contiguous portions (performance) l small fixed portions (flexibility) n File fragmentation and reorganization

Redundant Array of Independent/ Inexpensive Disks (RAID) RAID is a set of physical disk drives viewed by the OS as a single logical drive Data are distributed across the physical drives of an array Redundant disk capacity is used to store parity information, which guarantees data recovery RAID Levels: various levels of performance and redundancyRAID Levels –the disks are divided in strips: physical blocks, sectors, or similar –the strips are mapped round robin on the array –I/O requests can be processed in parallel strip 0 strip 4 strip 8 strip 12 strip 1 strip 5 strip 9 strip 13 strip 2 strip 6 strip 10 strip 14 strip 3 strip 7 strip 11 strip 15

Storage Management Storage Area Network (SAN) –Building a Storage Area NetworkBuilding a Storage Area Network –Fiber and IPFiber and IP Network Attached Storage (NAS) –SAN and NAS topologySAN and NAS topology –NAS and interoperabilityNAS and interoperability Comparison of SAN and NAS –SAN and NAS comparisonSAN and NAS comparison