[Beowulf] SSD prices - q: how many writes/erases???

Joe Landman landman at scalableinformatics.com
Thu Dec 18 10:12:25 EST 2008


Lux, James P wrote:

>> I can't find the Intel P/E cycle, but the Ridata units are 2x10^6 (2E+6).
>>
> 
> Is that the underlying device wearout life, or is it the apparent life at
> the "integrated unit"'s external interface.  For instance, if they had a

The latter I believe, as consumers (the mass market consumers) generally 
don't care about the former.

> wear leveler and some smart EDAC inside an ASIC that provides the interface,
> and just added extra capacity to account for the life.
> 
> After all, it's not like at N cycles, the device stops working.  It just
> starts working "less well" and throwing more errors, and I'll guess (since I
> don't have the data here in front of me) that there's a fair amount of
> variability, even within a single device.
> 
> Consider the testing needed to exhaustively verify the 2E6 number.. 16GB of
> 512 byte sectors.. That's 160E6 sectors, roughly.  They don't give an "erase
> time" spec, but let's just say 1 millisecond to make things easy.  So, to do
> one erase on ALL sectors takes 160,000 seconds, or about 2 days.
> 
> In a mere 4 million or so days, one could actually verify the erase life.

Of course, this is why they do the statistical testing.


> One can beat a single sector to death in 20,000 seconds or 6 hours.  But, is
> a single sector a valid test?  Nope.. You KNOW the EDAC is going to get in
> the way, not to mention that a single sector test doesn't address the
> variability across the device issue.  You'd probably want to sample, oh, 100
> or 1000 or so sectors of the 160 million, to get a reasonable statistical
> estimate. Now you're back in the days and weeks and months of testing (6000
> hours is the better part of a year) regime.

Yup.


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Joseph Landman, Ph.D
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