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I assume the local emonCMS is the "low-write" version on an SD card, The PHPfiwa take 5x as many writes to store the same data as a PHPfina because of the averaging.

Certain write intensive features had to be held back from the "low-write" version to help prevent premature SD card failure. You will also find data cannot be edited, corrected or backdated.

You can find many discusssions on this around the forum using search or read up on the "low-write emoncms" in the documentation on the emoncms repo

​Or you can switch to the full emoncms version if you add a hard-drive.

Paul

Thanks for your reply ;) I'm trying to read me up her, but theres a lot of info to understand ;)

I have recently set up a Pi2 with the "low-write" version using and SD card.  As expected, phpfiwa is not available.  There seem to be many advantages in using phpfiwa, especially for long-term analysis of power usage as I would like to do.  To do this the best option seems to be using an external hdd (or ssd to reduce power).

What is the future of phpfiwa?  With the recent development effort of emonPi using an SD card presumably most local logging will be done with phpfina.  Does this mean phpfiwa will fall off the radar and be less well supported in the future?  Or perhaps it will one day be supported on an SD card?

Just wanting to get a bit of an idea if it is worth me buying an external enclosure and ssd before logging too much data with the 'wrong' engine.

Anyone?

Since the development process in general is quite fluid it difficult to say with any certainty how things will evolve, by initial thoughts are hdd's can be very cheap, useful for other things and easily re-purposed or sold on so the potentially "wasted" financial investment can be quite minimal.

The data however could be perceived as more valuable (or less) depending on your own persuasion. Since the PHP feeds are quite a basic form the data could probably be converted rather than lost if it came to the crunch.

A while back a user complained about "being forced" to use the new feed engines rather than mySQL, I recall telling him that was not the case that despite the new engines being the prefered method, mySQL would probably always be supported since it is a very common database with a massive following and flexibility for integration etc. Recently the decision was made to completely remove the mySQL options so I was wrong to assume that. Despite my reasons still holding the outcome wasn't as i expected (or hoped for) so I can only speculate and have been known to be completely wrong! (that's a disclaimer too)

Any transition is likely to be slow I wouldn't expect anyone to be left high and dry.

The PHPfiwa feed has the averaging that can be "dropped during conversion" to another feed type that doesn't require it, rather than the other way round.

The current direction as I understand is too make emonCMS less write intensive specifically for lower SD card wear, there were plans to reintroduce the features currently missing from the low-write version but how (or if) that is implemented I'm not sure.

So yes the SD card is the current focus, as is the emonPi, therefore (reading between the lines) I would expect the missing features to become a priority and be compatible with existing PHPfiwa. 

I understand the same issue effects the SSD's also so I certainly wouldn't invest in a ssd just yet as the current high write rate could shorten it's life. The write rate will lower as will the prices so hold off for now.

Your (local) options IMO are to "just accept no averaging" for now or start logging PHPfiwa to a cheap spinning hdd, deferring the decision to buy a SSD or fully adopt a "SD card only" or take a chance on a full emoncms install on a SD card and hope it lasts longer than the development takes ( doing regular backups of course).

Personally I currently prefer to use a local hdd for full functionality and reliability but hope the development continues to reduce write rates to make a "full" SD card version possible as this would also make the 'price v longevity' investment of a SSD so much more viable too.

Paul

Thanks for detailed answer.  I think for now I will take your advice and use an existing spinning hdd I have lying around.  Once things stabilize a bit I will look at converting over to an SSD to save on power.

Regarding SSD wear, I think an SSD will last close to forever in home use.  My understanding is the memory used is much higher quality than used in SD cards.  Also, the controllers and wear-leveling algorithms are far more advanced in SSD drives.