Correcting a bit flip requires three extra (non-parity) bits.
00+000
01+011
10+101
11+110
STARTSIDEONTE(This)
In particular, this is known as a distance three Hamming code because
transforming one valid check-bit group to another valid check-bit group
requires flipping two different bits.
END-DELETING()
is known as an error-correcting code (ECC).
RAID 2
RAID 2 disks bit-stripe bytes across seven disks.
Four data disks and three parity disks.
The disk set forms an ECC over the data disks.
The three-disk overhead varies with the data disks, but is usually less
than RAID 1.
RAID 3
External error detection makes possible one-bit error recovery.
010?0101+0 → 01010101+0
Modern disks provide sector-level error detection.
RAID 3 uses n - 1 data disks and a parity disk for reliability.
Bit-striped bytes, but sector-level recovery.
But What of Latency?
Reducing latency via technology is hard and expensive.
Not so delay.
Latency usually responds to cleverly using current technology.
Load balancing, for example.
File systems are mainly responsible for reducing latency.
Summary
Disks provide an array abstraction with (cylinder, track, sector)
addressing.
And involve persistence.
Good performance requires handling latency and delay.
Delay can be handled simply (more or less) with redunpdancy.
From there come RAID devices.
Handling latency is the file system’s responsibility.