Re: SSD + RAID

On Mon, Feb 22, 2010 at 7:21 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Mon, Feb 22, 2010 at 6:39 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
>> Mark Mielke wrote:
>>>
>>> I had read the above when posted, and then looked up SRAM. SRAM seems to
>>> suggest it will hold the data even after power loss, but only for a period
>>> of time. As long as power can restore within a few minutes, it seemed like
>>> this would be ok?
>>
>> The normal type of RAM everyone uses is DRAM, which requires constrant
>> "refresh" cycles to keep it working and is pretty power hungry as a result.
>>  Power gone, data gone an instant later.
>
> Actually, oddly enough, per bit stored dram is much lower power usage
> than sram, because it only has something like 2 transistors per bit,
> while sram needs something like 4 or 5 (it's been a couple decades
> since I took the classes on each).  Even with the constant refresh,
> dram has a lower power draw than sram.

Note that's power draw per bit. dram is usually much more densely
packed (it can be with fewer transistors per cell) so the individual
chips for each may have similar power draws while the dram will be 10
times as densely packed as the sram.