Flash writings limit?

Hello to every body,

Is it harmful to the flash memory if the whole filesystem tree in
linux is intalled on flash (including /tmp /var and other directories with a high rate of writing operations) ? I have Strata Flash with JFFS2 installed.

Thank you in advance

It depends how much you actually write to those directories, but yes - it's advisable to put them elsewhere. The iPAQ uses ramfs for /tmp and some of the subdirectories of /var - that seems like a sensible plan.

--
dwmw2

Thanks a lot. How do you set this ram partitions at boot time? I am considering two options:

1) Have a compressed image in flash and load it with a loader in RAM
2) Execute a script in init to set the ramdisks partitions

Which one do you think is best?

Thanks a lot again

Howdy,

Well, it would be horribly slow when system logs etc in /var are written to flash, but in practice you can write to Flash an incredible number of times before it will become unreliable. In my experience the first thing that happens with age is that the erase cycles become slower and may increase from around 500ms to as much as 15s, but the device will still work reliably. This aging happens quite quickly actually - a few hundred erase cycles and the device will be significantly slower than when new. (I have seen and fixed many erase algorithms that do not allow sufficient erase time for old parts!).

When the manufacturer guarantees a 100 000 cycle limit, you can probably expect an average lifetime of 1 000 000, so in a consumer device with a life expectancy of around 3 years, you probably need not worry about the Flash lifetime, even if all the Linux logs and crud are written to Flash, since the keyboard or connectors will wear out before the flash does. In the case of a plug-in flash card for instance, the card will probably suffer mechanical failure long before the electrical parts fail, either because of the connector wearing out, or somebody stomping on the card...

It would be a different matter for medical/military applications though, where one cannot rely on average performance but needs to look at the worst case scenario. So, if you are working on a control system for an ICBM or something, then please look at the 100 000 limit...

Herman Oosthuysen
E-mail: [email protected]
Phone: 403+569-5687, Fax: 403+235-3965