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File management - PowerPoint PPT Presentation

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File management
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  1. File management

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

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

  4. File allocation table (FAT) • Pre allocation vs dynamic allocation • 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: • variable, large contiguous portions (performance) • small fixed portions (flexibility) • File fragmentation and reorganization File allocation

  5. strip 0 strip 1 strip 2 strip 3 strip 4 strip 5 strip 6 strip 7 strip 9 strip 10 strip 11 strip 8 strip 13 strip 15 strip 14 strip 12 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 redundancy • 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

  6. Storage Management • Storage Area Network (SAN) • Building a Storage Area Network • Fiber and IP • Network Attached Storage (NAS) • SAN and NAS topology • NAS and interoperability • Comparison of SAN and NAS • SAN and NAS comparison