NAND Write operations

[Charles Manning]

You'd probably do far better to ask questions like this on the linux-mtd list 
or similar.

I'm the author of the yaffs file system, so I can answer some of your 
questions though. 

Pretty much all flash file systems or flash management layers such as UBI 
perform at least some degree of wear levelling. This means that there is some 
sort of logical to physical, or other, policy so that the writes don't happen 
in the same place. That means those writes to a certain file will end up 
being spread across many different blocks, thus meaning that writes to one 
particular file won't wear out one part of flash.

And yes, the endurance depends on the type of flash. Some are of the order of 
10^6, some are only 10^3. 

Worst I've seen is 10^2, but that was for a "bootloader" section and not 
designated for file usage.

-- CHarles

On Tuesday 13 April 2010 07:58:22 Cathey, Jim wrote:
> I was concerned enough that our "/" fs is read-only,
> with symlinks for everything interesting down into
> /tmp/etc instead.  The rcS script made the initial
> set from a bunch of template files.
>
> It, of course, was an embedded device that happened
> to be based on Linux, not some sort of "embedded Linux"
> device where J. Random Developer would expect to function
> happily.
>
> Last I heard, the worst of the NAND flash devices was
> on the order of 10^3-10^5 writes, not 10^6.
>
> -- Jim
>
> -----Original Message-----
> From: busybox-bounces at busybox.net [mailto:busybox-bounces at busybox.net]
> On Behalf Of Sameer Naik
> Sent: Monday, April 12, 2010 12:03 PM
> To: BusyBox Developer List
> Subject: NAND Write operations
>
> Hi,
> This may not be the right place to ask this question, but i only ask
> this because i believe most of the developers on this list work
> primarily with embedded systems. So here goes it.
>
> Normally on a linux system network configuration related files like
> resolv.conf and ifcfg-eth*, etc are stored in the /etc folder. These
> files are normally updated at boot or precisely when the network is
> configured. NAND memory have a ~100K write cycles before which write
> could start failing.
> This number is rather very large, hypothetically even if the network
> is configured 10 times a day the flash is good for around 27 years
> (100000 / (365 * 10)).
>
> Secondly, considerable amount of fragmentation could occur due to
> small updates on the file system
>
> I may be getting a little paranoid here, but how much is this of
> cencern on a production system.
>
> Regards
> ~Sameer
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