NetBSD-Users archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

Re: FFSv2 log option with SD card




On 22/02/2020 10:05 pm, Sad Clouds wrote:
On Sat, 22 Feb 2020 11:43:42 +0100
tlaronde%polynum.com@localhost wrote:

On Sat, Feb 22, 2020 at 08:24:18AM +0000, Sad Clouds wrote:
On Sat, 22 Feb 2020 11:37:35 +1100
MJ <mafsys1234%gmail.com@localhost> wrote:

On 22/02/2020 4:28 am, Sad Clouds wrote:
Hi, is it advisable to NOT enable log option for FFSv2 that
resides on SD card due to flash memory wearing out in those
regions, or does it make no practical difference because of
built-in wear levelling?

How long's a piece of string?

Wear levelling just evens out the wear... surprise. It doesn't
account for the overall wear.
Well the SD card contains a general purpose file system, so I'm
expecting some wear on it as data is written over time (normal
desktop computer use). I wasn't sure if FFSv2 logging would
significantly shorten the life span. But I'm guessing it may not be
such a big issue for quite a few years.
 From what I have gathered from infos taken here and there, it will
depend on how much percentage the data is occupying on the SD card. If
there is enough empty room on the SD card, the card is optimized so
that new data is written "elsewhere" so that new writes impact other
sectors. The much you have not used sectors, the less the sectors are
overwritten and thus the longer the card will survive.

The error is taking a card that is too small and fits too closely the
amount of data being retained.
Not sure how this would work. If the card is brand new, then I guess it
knows the memory cell is empty, but once you have filled the card and
then deleted most of the files, file system will mark those blocks of
data as free, but the card doesn't know the data has been deleted. I
don't think there is anything like TRIM command.


No there's not a TRIM for SD, the controller on them is limited. What tlaronde was getting at, I thinkj, is that its wear levelling attempts to spread data across the card not constantly writing to the one spot. However, should your SD card fill, the controller is less and less likely to be able to move data around to mitigate wear.

SD cards are cheap, purchase one with excess capacity to prevent you filling it up.




Home | Main Index | Thread Index | Old Index