RAID

Question 1

level 0

Answer 1

block striping; write one block to each disk
therefore each disk gets a fraction of the total data rather than a complete copy

Question 2

level 1

Answer 2

mirroring: having redundancy by writing to n disks at once therefore if one of them fails then you have another copy

Question 3

level 4

Answer 3

block striping (level 0) + parity bit: if an error occurs then you can identify it on a block basis
every write writes to the parity disk

Question 4

level 5

Answer 4

block striping + parity bit across all disks

Question 5

what is a positive of level 5 compared to 4

Answer 5

reduces bottleneck and increases fault tolerance

Question 6

level 6

Answer 6

level 5 with error correcting code

Question 7

what is raid and what does it actually do

Answer 7

Redundant Array of Independent/Inexpensive Disks; combines multiple physical hard drives into a single logical unit to improve performance, fault tolerance, or both.

Question 8

what is a time based negative of raid

Answer 8

average time to repair can be long (though more infrequent) as you have to write the contents to multiple disks

Question 9

what is a negative based on power failures

Answer 9

power failures can cause blocks to fail

Question 10

how do we avoid power failures completely fucking the system

Answer 10

e.g. ssd can have data written to them before the power goes off completely therefore we use them with disks
the ssd now acts as a cache

Question 11

how can we stop read operations from becoming delayed

Answer 11

decouple writes from the disk makes reads quicker
we store the writes in cache and do them later as theyre not needed right now unlike reads