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Mass-Storage Systems (RAID Structure (RAID schemes improve performance and…
Mass-Storage Systems
RAID Structure
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RAID within a storage array can still fail if the array fails, so automatic replication of the data between arrays is common
RAID schemes improve performance and improve the reliability of the storage system by storing redundant data
Striped mirrors (RAID 1+0) or mirrored stripes (RAID 0+1) provides high performance and high reliability
Block interleaved parity (RAID 4, 5, 6) uses much less redundancy
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Solid-State Disks
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No moving parts, so no seek time or rotational latency
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Storage Area Network
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Easy to add or remove storage, add new host and allocate it storage
Disk scheduling
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I/O request includes input or output mode, disk address, memory address, number of sectors to transfer
OS maintains queue of requests, per disk or device
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Disk management
Low-level formatting
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Each sector can hold header information, plus data, plus error correction code
To use a disk to hold files, the operating system still needs to record its own data structures on the disk
Partition the disk into one or more groups of cylinders, each treated as a logical disk
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Hard disks
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Commonly 3.5”, 2.5”, and 1.8”
SSTF
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Shortest Seek Time First selects the request with the minimum seek time from the current head position
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Storage Array
Can just attach disks, or arrays of disks
Storage Array has controller(s), provides features to attached host(s)
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Memory, controlling software
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RAID, hot spares, hot swap
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