[maemo-users] 2Gb internal storage on N810

From: Nils Faerber nils.faerber at kernelconcepts.de
Date: Sat Jun 27 13:40:32 EEST 2009
Alexandru Cardaniuc schrieb:
> Hi All!

> Just got myself N810 and have a couple of questions.
> What is the 2Gb internal storage? Is it a built-in non-replaceable SD
> card? Wikipedia states that: "limited number of writes can be made
> before failure" on SD cards. So, is the future failure an issue? Should
> I use it less often, like not use it as a virtual memory? 
> What about the 256Mb internal flash storage? Is it susceptible to wear?
> :)
> So, I was thinking about getting an external SD card and booting from
> it, and also running everything from it. It's easy to replace it if it
> fails. 

Well, all flash has only a limited number of erase/write cycles. The
internal flash of the N810 is for one a built-in SD card and the other
is built-in NAND chip flash. They both can wear and show errors. The
good thing about NAND is that NAND is expected to have errors and all
hard- and software that deals with NAND must be capable of handling such
error, i.e. remapping bad blocks. For NOR flash you usually do not have
this and a bad block can lead to system malfunction. On NAND just the
size shrinks.
For SD cards which usually are also based on NAND flash the built-in
controller chip will automatically handle the remapping without letting
you recognise it.

So buttomline is, it is safe to use flash based devices as long as you
do not very intensively (re-)write data to them - e.g. having a swap
space on internal chip-flash would probably not be a very clever idea.
But for normal use it is perfectly fine. If you put an EXT2 or EXT3
filesystem on an SDcard please remember to mount with the "noatime"
option in order to prevent frequent inode updates which could wear out
your device too fast.

And finally you should take the average number of write cycles until
failure into account. All chips specify this and it means the average
for per eraseblock. Numbers of 10.000 to 100.000 or even 1.000.000 are
possible. Most filesystems used on NAND and also the controller chips in
SDcards do wear levelling, which means they distribute the erase cyles
over the chip / partition as much as possible. So with a 2GB SDcard and
not too often writes the probability that the same eraseblock is erased
again is pretty low and thus 100.000 cycles is a very long time -
usually much much longer than the lifetime of the other parts of the device.

Finally this may also be an interesting reading:

> Is there any difference in speed if I get a microSD card and use it with
> the miniSD adapter as opposed to getting a miniSD card? The reason for
> getting microSD is that I can use it on more of my devices...

This depends on the controller chip, chip type and chip organisation
(interface width) used in the card. I do not think that there is a
general rule that micro SD is faster or slower. It is interfacewise
completely identical to a big SDcard and can run on the same clockrates etc.

> Thanks in advance for help.
  nils faerber

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