Disk and File Organization Flashcards
magentic storage
hard disk drives and floppy disks use magnetic fields to store data on a rotating disk. the data is later accessed using a read/write head that moves across the surface of the disk
flash storage
solid state drives and usb drives use non-volatile memory chips to store data. flash storage can be accessed electronically, this makes it faster and more reliable than magnetic storage
non-volatile
refers to the ability of a type of memory to retain its data even when the power is turned off
redundant array of independent disks (raid)
disk organization technique to manage a large number of disks
mirroring
duplicate every disk; every write is carried out on both disks and read can use either disk
bit-level striping
split the bits of each byte across multiple disks
block-level striping
with n disks, block i of a file goes to disk (i mod n) + 1
parity blocks
a parity block’s ith bit is the XOR (exclusive or) of the ith bits of all the blocks in the set (reverse to get a block’s data back)
raid 0
disk arrays with striping at the level of the blocks, but no redundancies
- use when data safety is not important
raid 1
disk mirroring with block striping (has a copy of each disk)
- better write performance than raid 5
raid 4
disk arrays with striping across multiple disks and a dedicated parity block
- not useful for reads
- bad for writes
raid 5
partitions data and parity among all N+1 disks, rather than storing data in N disks and parity in 1 disk
- for applications where write are sequential and large and new large amounts of data storage
raid 6
similar to raid 5 but stores 2 error correction blocks instead of a single parity block to guard against multiple disk failures
heap
record can be placed anywhere in the file where there is space
free space map
an array containing 1 entry for each block in the relation where each entry is a few bits to 1 byte in size; each bloc contains a fraction indicating haw much space in the block is free
