[clug] Kernel without initramfs

[David Tulloh]

Daniel Pittman wrote:
> Robert Edwards <bob at cs.anu.edu.au> writes:
>
>   
>> I notice in one of your earlier posts that you may be using ext3 on
>> your CF device. May I suggest that it is a bad idea to use ext3 in
>> particular and most other journalling FS's in general on a
>> "flash"-based device?
>>     
>
> You can suggest that, but you would be wrong, since one of your
> underlying assumptions is incorrect.
>
>   
>> For the writable parts work out if you can afford to write to a
>> RAM-base FS and then copy important data back to non-volatile
>> storage. Logging etc., if possible, should be to an external logging
>> server.
>>     
>
> That is generally good advice.
>
> Anyway, to the specifics of your suggestion: the reason that ext3 is no
> more likely to cause a CF card trouble than any other filesystem is
> simple, and that is that the CF card performs wear levelling internally.
>
> JFFS is designed for direct access to the flash hardware, in which there
> is no hardware wear levelling, so it is essential to balance writes.
>
>   
Regardless of if the write leveling is performed in software or hardware 
you will get more wear if you do more writes.  Hammering away with 
journaling information is going to create a fantastic number of writes.  
100,000 cycles isn't that many if you want the product to last eight 
years, less if you factor in that a chip wears unevenly as it get full.  
My personal experience has also been that sectors wear out before the 
quoted minimum number of cycles.

Most embedded systems I have used to go to considerable effort to have a 
read-only file system and extensively use tmpfs.  Actual writes are rare 
and controlled, development is done over a NFS mount.  Though most of 
the devices I have used don't bother with wear leveling, they tend to 
save configuration information and not much else.



David