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2Gb internal storage on N810

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cardaniuc at gmail

Jun 26, 2009, 8:04 PM

Post #1 of 11 (2095 views)
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2Gb internal storage on N810

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.

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...

Thanks in advance for help.

--
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because the answer is not separate from the problem."
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nils.faerber at kernelconcepts

Jun 27, 2009, 3:40 AM

Post #2 of 11 (1955 views)
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Re: 2Gb internal storage on N810 [In reply to]

Alexandru Cardaniuc schrieb:
> Hi All!
Hi!

> 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:
http://en.wikipedia.org/wiki/Flash_memory

> 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.
Cheers
nils faerber

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hendrik at topoi

Jun 27, 2009, 7:41 AM

Post #3 of 11 (1959 views)
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Re: 2Gb internal storage on N810 [In reply to]

On Sat, Jun 27, 2009 at 12:40:32PM +0200, Nils Faerber wrote:
>
> 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.

But when it does start to fail, it will probably have so many bad blocks
that it fails completely. THis kind of redundancy and error correction
make a system resilient to damage, but also make it more brittle when
it does start to crack. Backups are always useful.

> Finally this may also be an interesting reading:
> http://en.wikipedia.org/wiki/Flash_memory
>
> > 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.

What does matter is the so-called category of the SD card, which is a
measure ot its speed. The "category" is usually a number written inside
a C on the card itself. More is better. I think the N800 can benefit
from SD speed up to category 6 or 8 or so. I don't know if the N810 is
different. I have category 6 8G cards in my N800.

Category 2 cards sold in drug stores (and even some mass-market
consumer electronics dealers) seem to have similar prices to category 6
cards at on-line computer-electronics dealers. There's an enormous, and
largely random, variation in prices even within one retail store. It's
worth shopping around.

-- hendrik
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lakestevensdental at verizon

Jun 29, 2009, 8:12 AM

Post #4 of 11 (1935 views)
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Re: 2Gb internal storage on N810 [In reply to]

While some express concern/fear about memory errors on flash cards,
there seems to be little mention of such problems from n800 users who
have been using replaceable flash cards for several years. So while
there probably is some wall when these things may start to happen for
n810s, it's still a bit out in the future. For n800s users, there's the
simple fix of swapping a new card.
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cardaniuc at gmail

Jun 29, 2009, 9:09 PM

Post #5 of 11 (1934 views)
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Re: 2Gb internal storage on N810 [In reply to]

"lakestevensdental [at] verizon" <lakestevensdental [at] verizon> writes:

> While some express concern/fear about memory errors on flash cards,
> there seems to be little mention of such problems from n800 users who
> have been using replaceable flash cards for several years. So while
> there probably is some wall when these things may start to happen for
> n810s, it's still a bit out in the future. For n800s users, there's
> the simple fix of swapping a new card.

Easy fix for replaceable cards, but how about built-in 256MB flash
memory?

--
"Individual rights are not subject to a public vote; a majority has
no right to vote away the rights of a minority; the political
function of rights is precisely to protect minorities from
oppression by majorities (and the smallest minority on earth is the
individual)."
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eero.tamminen at nokia

Jul 21, 2009, 12:53 AM

Post #6 of 11 (1708 views)
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Re: 2Gb internal storage on N810 [In reply to]

Hi,

ext Alexandru Cardaniuc wrote:
>> While some express concern/fear about memory errors on flash cards,
>> there seems to be little mention of such problems from n800 users who
>> have been using replaceable flash cards for several years. So while
>> there probably is some wall when these things may start to happen for
>> n810s, it's still a bit out in the future. For n800s users, there's
>> the simple fix of swapping a new card.
>
> Easy fix for replaceable cards, but how about built-in 256MB flash
> memory?

As far as I remember correctly, on average it has enough write cycles
that you should be able to write to it *constantly* for tens of years.
I doubt the rest of device will last that long. :-)

Except for RSS, email etc refreshes which results are stored under
/home/ and operations for files on /home/MyDocs, there shouldn't be
much writes to it though. If you have Flash enabled in Browser, but
no memory card, the video streaming is buffered on that too.

Real reason for avoiding frequent writes / disk churn on rootfs is that
this would trigger JFFS2 garbage collecting much more frequently which
can *really* slow down your device:
https://bugs.maemo.org/show_bug.cgi?id=2615

The internal 2GB memory card in N810 has less write cycles than
the roots. Because it's larger, it can spread the writes over more
blocks i.e. wearing shouldn't be a problem for that either.

Btw. Personally, I wouldn't enable swap on it (from Control panel)
though, at least constantly, for following reasons (ordered from more
important to less important):
1. with constant swap file writes, it's much easier to
accidentally cause the card FAT file system to get corrupted
2. there's a performance slowdown (although swap allows running
some use-cases that wouldn't be otherwise possible)
(3. Flash wearing)

If you want swap, I would suggest a fast SD card with a separate
_partition_ for swap and some hacking on the device startup scripts
to support this.

- Eero
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dufkaf at seznam

Jul 23, 2009, 12:45 PM

Post #7 of 11 (1675 views)
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Re: 2Gb internal storage on N810 [In reply to]

Eero Tamminen wrote:

> 1. with constant swap file writes, it's much easier to
> accidentally cause the card FAT file system to get corrupted
...

> If you want swap, I would suggest a fast SD card with a separate
> _partition_ for swap

AFAIK since version 2.4 of linux kernel, swapping to file no longer goes
via filesystem code at all and speed is similar/same to swapping to
block device directly. Kernel swapping code makes mapping for blocks
belonging to swap file on the beginning and then uses underlying block
device directly (both for speed and for deadlock prevention). If the
file is not heavily fragmented speed should be the same. Fragmentation
is visible in kernel log when swap file is enabled (number of extents).

As for corruption I'm not sure but I'd say it is not an issue too since
file is already allocated and filesystem code is not used when swapping.

Frantisek
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dufkaf at seznam

Jul 23, 2009, 12:50 PM

Post #8 of 11 (1679 views)
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Re: 2Gb internal storage on N810 [In reply to]

Frantisek Dufka wrote:
> Eero Tamminen wrote:
>> If you want swap, I would suggest a fast SD card with a separate
>> _partition_ for swap
>
> AFAIK since version 2.4 of linux kernel, swapping to file no longer goes
> via filesystem code at all and speed is similar/same to swapping to
> block device directly.

more details here, 2.6 kernel is better
http://lkml.org/lkml/2005/7/7/326

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gary at eyetraxx

Jul 23, 2009, 2:50 PM

Post #9 of 11 (1677 views)
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Re: 2Gb internal storage on N810 [In reply to]

Frantisek Dufka wrote:
> AFAIK since version 2.4 of linux kernel, swapping to file no longer goes
> via filesystem code at all and speed is similar/same to swapping to
> block device directly.

That is true but in this case, AFAIK, with the maemo control panel
you're building a swap file on a FAT32 file system. That would most
likely result in a different performance metric than if you built a swap
file on top of ext3 or used a raw swap slice. Someone please correct me
if I'm wrong, however, as I've considered partitioning up my own SD
cards. I do know that the I/O throughput varies greatly from card to
card which is why the high speed SDHC cards are more expensive depending
on the speed class. q.v. http://www.sdcard.org/developers/tech/speed_class

-Gary
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matan at svgalib

Jul 23, 2009, 4:34 PM

Post #10 of 11 (1685 views)
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Re: 2Gb internal storage on N810 [In reply to]

On Thu, 23 Jul 2009, Gary wrote:

> Frantisek Dufka wrote:
>> AFAIK since version 2.4 of linux kernel, swapping to file no longer goes
>> via filesystem code at all and speed is similar/same to swapping to
>> block device directly.
>
> That is true but in this case, AFAIK, with the maemo control panel
> you're building a swap file on a FAT32 file system. That would most
> likely result in a different performance metric than if you built a swap
> file on top of ext3 or used a raw swap slice. Someone please correct me
> if I'm wrong,

You are wrong. A simplified version of what happens:
At swapon time, the kernel builds a table in RAM of where all the blocks
of the swap file are. Later during swap in/out the table is used and
filesystem is ignored. So filesystem might affect the time to run
swapon, which happens once at boot time, but does not matter to the swap
performance after that.

--
Matan Ziv-Av. matan [at] svgalib

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eero.tamminen at nokia

Jul 24, 2009, 12:01 AM

Post #11 of 11 (1674 views)
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Re: 2Gb internal storage on N810 [In reply to]

Hi,

ext Frantisek Dufka wrote:
>> If you want swap, I would suggest a fast SD card with a separate
>> _partition_ for swap
>
> AFAIK since version 2.4 of linux kernel, swapping to file no longer goes
> via filesystem code at all and speed is similar/same to swapping to
> block device directly. Kernel swapping code makes mapping for blocks
> belonging to swap file on the beginning and then uses underlying block
> device directly (both for speed and for deadlock prevention). If the
> file is not heavily fragmented speed should be the same. Fragmentation
> is visible in kernel log when swap file is enabled (number of extents).

I think the file system (especially one as trivial as FAT) overhead is
trivial compared the Flash writing speed of the card.

> As for corruption I'm not sure

At least there were much more corruption reports from people who
had enabled swap than from ones that hadn't. (It's possible that
they are heavier users and therefore have more changes to mess
things up with accidental USB cable removal, taking card out while
it's still being used etc. But there were no re-producible use-cases
for verifying these things.)

> but I'd say it is not an issue too since file is already allocated
> and filesystem code is not used when swapping.

<speculation>
Whenever you do a write to a Flash based media, the data is written
somewhere else and the old block is GCed (with the HW API provided
by the memory cards kernel just doesn't see it). Also, I think
the Flash blocks could be larger than the ones used by kernel
internally for swap (4kB?) or the VFAT allocation units, or they might
not be aligned....?

So... It's possible that swap can affect the contents of rest of
the VFAT, especially if the swap file was made on a fragmented VFAT.
</speculation>

- Eero
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