File management File Systems Architecture access methods logical

File management

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

File sharing and blocking n File sharing – – n 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 block data IRG block data IBG IBG IRG

File allocation table (FAT) n Pre allocation vs dynamic allocation n Portion size n – – n 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) 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 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 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 Network – Fiber and IP • Network Attached Storage (NAS) – SAN and NAS topology – NAS and interoperability • Comparison of SAN and NAS – SAN and NAS comparison