DDR3 Memory의 RAS(Reliability Availability Serviceability)/AMP(Advanced Memory Protection)
1. Spare
두 개 채널을 데이터 I/O에 사용하고, 한 개 채널을 여분으로 보유하여 데이터를 저장하던 채널 중 문제가 발생하는 경우 대체하여 사용하게 된다.
2. Mirror
두 개 채널을 데이터 I/O에 사용하는데, 동일한 내용을 복제하여 사용하기에 실 가용 용량은 절반이다.
미러링 하기 위해 짝수로 사용되어야 하기에 세번째 채널은 사용하지 않는다.
3. Lockstep
두 개 채널을 데이터 I/O에 사용하며, 두 개 채널 전체를 마치 하나의 메모리 처럼 I/O를 발생시키는 기술로 일반 DDR3가 4bit 오류를 보정 가능한 반면, 8bit 오류를 보정 가능하게 된다. 하지만 약 40% 정도의 성능 저하를 가져올 수 있어 사용 목적을 잘 선택해야 하겠다.
Lockstep Memory mode uses two memory
channels at a time, stores half the cache line in one DIMM on one
channel and the other half on the next, and offers an even higher level of
protection.
In lockstep mode, two channels operate as a
single channel
- each write and read operation moves a data word two channels wide.
- are accessed simultaneously, but different
contents are written to each. The cache line is split across both channels so different parts of the
same cache line are stored in multiple places.
Both channels split the cache line to provide 2x 8-bit error detection and 8-bit error correction within a single DRAM.
In three-channel memory systems, the third
channel is unused and left unpopulated.
The Lockstep Memory mode is the most
reliable, but it reduces the total system memory capacity by a third in 3 DIMM
per channel designs.
Memory modules must be
identical in size, speed, and technology in corresponding slots.
The following applies when in memory lockstep mode:
• 2 channels
operating in lockstep (cache line is split across both channels), 3rd channel
is unused
• Both
channels must be populated identically
• x8 SDDC is
supported (x8 SDDC is supported only in lockstep mode)
• No
mirroring support in this mode
• Compared
to a 3-channel configuration with only x4 SDDC, reliability increases, but
performance drops and capacity drops (only 2 channels used)
Reliability, availability and serviceability (computer hardware)
http://en.wikipedia.org/wiki/Reliability,_availability_and_serviceability_(computer_hardware)
