Re: SSD performance

On Sun, 25 Jan 2009, Gregory Stark wrote:

> david(at)lang(dot)hm writes:
>
>> they currently have it do a backup immediatly on power loss (which is a safe
>> choice as the contents won't be changing without power), but it then powers off
>> (which is not good for startup time afterwords)
>
> So if you have a situation where it's power cycling rapidly each iteration
> drains the battery of the time it takes to save the state but only charges it
> for the time the power is on. I wonder how many iterations that gives you.

good question.

assuming that it's smart enough to not start a save if it didn't finish
doing a restore, and going from the timings in the article (~20 min save,
~15 min load and 4 hour battery life)
you would get ~12 cycles from the initial battery
plus whatever you could get from the battery charging (~3 hours during the
initial battery time)

if the battery could be fully charged in 3 hours it could keep doing this
indefinantly.

if it takes 6 hours it would get a half charge, so 12+6+3+1=22 cycles

but even the initial 12 cycles is long enough that you should probably be
taking action by then.

in most situations you are going to have a UPS on your system anyway, and
it will have the same type of problem (but usually with _much_ less than 4
hours worth of operation to start with)

so while you could loose data from intermittent power, I think you would
be far more likely to loose data due to a defective battery or the CF card
not being fully seated or something like that.

David Lang