2.11BSD on two RL02 drives? Probably not, but...

Guy Sotomayor Jr ggs at shiresoft.com
Fri Aug 4 15:32:15 CDT 2017


> On Aug 4, 2017, at 1:27 PM, ben via cctalk <cctalk at classiccmp.org> wrote:
> 
> On 8/4/2017 12:49 PM, Warner Losh via cctalk wrote:
>> On Fri, Aug 4, 2017 at 12:36 PM, Al Kossow via cctalk <cctalk at classiccmp.org
>>> wrote:
>>> 
>>> 
>>> On 8/4/17 11:14 AM, Warner Losh via cctalk wrote:
>>>> most SD cards can easily handle 100-200 writes
>>> 
>>> The issue would be things like the swap partition on a unix disk
>>> or whatever the equivalent is under RSX
>>> 
>> Right. But since Flash devices have a FTL that translates writes to new
>> locations in the NAND each time a logical block is written, there's no
>> issue here. This issue with swap hasn't been an issue with NAND flash since
>> early ~8MB CF cards (which is now almost 20 year old technology).
>> I have a lot of miles using CF and SD cards in embedded systems, using both
>> commercial grade and industrial parts since 2000 or so. I find it hard to
>> believe that RSX could generate 128GB of data enough times, even in a
>> swapping environment, to wear a card like that out. Even a more modest 8GB
>> would take a while to wear out under 100% write workload, which swapping
>> never is (since there's always readback for at least some of the pages
>> swapped out). Though I did base my computations on 1MB/s being the fastest
>> that Q-Bus can go, but that was my remembered performance from 3 decades
>> ago since I couldn't find an answer to that question with a quick google. I
>> shipped systems that were 100's if not 1000's times faster than the
>> pdp-11's that could generate much more data traffic to SD and CF cards, and
>> had very very few CF cards wear out. SD cards when we shipped needed to be
>> not the smallest capacity on the market to do well and even there only a
>> few cards wore out while I was doing this with them...
>> Warner
> 
> With everything @ 3.3 volts, you might as well use a ram dick cache
> and back up dirty blocks on power fail, or power down, or reboot, as
> a small battery would last forever, while main system is down.
> 
> 

Use MRAM (non-volatile) and behaves just as well as SRAM.  That way you don’t
have to deal with the battery issues.

TTFN - Guy



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